Polyol-based polymers

ABSTRACT

The present invention provides inventive polyol-based polymers, materials, pharmaceutical compositions, and methods of making and using the inventive polymers and materials. In certain aspects of the invention, an inventive polymer corresponds to a polymer depicted below. Exemplary inventive polymers includes those prepared using polyol units (e.g., xylitol, mannitol, sorbitol, or maltitol) condensed with polycarboxylic acid units (e.g., citric acid, glutaric acid, or sebacic acid). The inventive polymers may be further derivatized or modified. For example, the polymer may be made photocrosslinkable by adding methacrylate moieties to the polymer.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Grant No.MCB0509923 awarded by the National Science Foundation. The governmenthas certain rights in this invention.

RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119(e) to U.S.provisional patent application, U.S. Ser. No. 60/930,606, filed May 17,2007, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Synthetic biodegradable polymers have significant potential in variousfields of bioengineering, such as tissue engineering and drug delivery.Synthetic biodegradable polymers are used as components in a variety ofbiomedical devices, such as, for example, implants, pacemakers, heartvalves, artificial joints, tubing, shunts, dialyzers, oxygenators,dental materials, tablet coatings, drug delivery devices, sutures,staples, adhesives, and the like. The design of these biomaterials ischallenging because of the application-specific requirements on thephysical and chemical properties of the biomaterials, includingmechanical compliance, strength, degradation, biocompatibility, etc. Forexample, synthetic biodegradable polymers that are designed asreplacements for soft and hard tissues must sustain and recover fromvarious stressors and deformations. Ideally, the material shouldresemble the mechanical properties of the tissues found at theimplantation site to prevent mechanical irritation and not compromisethe structural integrity of target tissues and organs. Biodegradablepolymers whose properties resemble that of the extracellular matrix, asoft, tough, and elastomeric proteinaceous network, provide the bestmechanical stability and structural integrity to tissues and organs. Todate, such elastomeric biomaterials include hydrogels (for example, Leeet al., Macromolecules (2000) 33:4291-4294; Temenoff et al., J. Biomed.Mater. Res. (2002) 59:429-437), elastin-like peptides (for example, vanHest et al., Chem. Comm. (2001) 19:1897-1904; Welsh et al.,Biomacromolecules (2000) 1:23-30), polyhydroxyalkanoates (PHAs) (forexample, Poirier et al., BioTechnology (1995) 13:142-150; Sodian et al.,Tissue Eng. (2000) 6:183-187), and tough biodegradable elastomers suchas poly(diol-citrate) (PDC), poly(glycerol-sebacate) (PGS),poly(D,L-lactide-co-ε-caprolactone), and poly(ε-caprolactone).

There remains a need in the art for synthetic biodegradable polymerswith a wide range of chemical and physical properties for use inbioengineering.

SUMMARY OF THE INVENTION

The present invention describes a platform for preparing syntheticpolyol-based polymers, ranging from hydrogels to hydrogel elastomers totough elastomers. These polyol-based polymers are typicallybiodegradable. These polymers may have one or more of the followingcharacteristics: (1) multifunctional to allow the formation of randomlycrosslinked networks and a wide range of crosslinking densities; (2)nontoxic; (3) components (e.g., monomers or degradation products) thatare endogenous to the human metabolic system; (4) approved by the U.S.FDA or other governmental regulatory office; and (5) inexpensive toprepare. In certain embodiments, the inventive synthetic polyol-basedpolymer is based on xylitol. The inventive polymers may be furtherprocessed (e.g., cross-linking, derivatization) to prepare novelmaterials.

Specifically, the present invention provides novel polymers fromcondensing and/or cross-linking polyols with polycarboxylic acids andfurther materials produced from these polymers. The inventive polymersmay be linear or branched polymers. The polymers are, in certainembodiments, biodegradable and/or biocompatible. Typically, thepolyol-based polymers are of the formula:

wherein Q, L, Z, W, R^(A), j, k, m, n, or p are as defined herein. Incertain embodiments, the polymer is of the formula:

wherein Q, Z, W, s, m, n, or p are as defined herein. In certainembodiments, the polymer is based on the polyol, xylitol, sorbitol,mannitol, or maltitol. In certain embodiments, the polyol is polymerizedwith a dicarboxylic acid such as sebacic acid.

The invention provides methods of preparing the inventive polymers andmaterials as well as various methods of using the inventive polymers andmaterials. The invention also provides pharmaceutical compositionscomprising an inventive polymer or material, and a biologically activeagent.

The present invention provides inventive polyol-based polymers which mayhave one or more of the following characteristics: (1) the inventivepolymer is made from naturally occurring monomers; (2) the inventivepolymer is biodegradable; (3) the inventive polymer is composed ofbiocompatible monomers (e.g., the pharmacokinetics and pharmacodynamicsof the monomers are characterized, and found non-toxic, in humans oranimals; and/or be approved by the U.S. Food and Drug Administration assafe for use in humans or medical applications); (4) one or more, orall, of the components of the in vivo degraded polymer is endogenous tothe human metabolic system, (5) the inventive polymer is inexpensive tomake (e.g., the polymerization to provide the inventive polymer can beachieved without the use of solvents; the production of the monomers andthe inventive polymer can easily be scaled up; the inventive polymer issynthesized rapidly (e.g., rapid polymerization)); (6) the inventivepolymer is prepared without using harsh solvents, reagents, and/orconditions (e.g., “neat” reaction mixtures; room temperaturepolymerization, low temperature polymerization); (7) the inventivepolymer can be polymerized in situ (e.g., in vivo); (8) the inventivepolymer is a hydrogel; (9) the inventive polymer is an elastomer; (10)the inventive polymer is transparent; (11) the inventive polymermaintains a high level of surface- and/or bulk-functionality (e.g.,exposed and/or unprotected hydroxyl and carboxylate functional groups);(12) the inventive polymer comprises an intra-network of hydrogenbonding; (13) the inventive polymer permits encapsulation ofbiologically active agents; (14) the inventive polymer has protein/celladhesion properties; (15) the inventive polymer is injectable; and/or(16) the inventive polymer is easily modifiable, and can be used as aplatform for the fabrication of other novel materials with uniquemechanical properties. The inventive polymers may be further modified toform new materials. In certain embodiments, the polymer is cross-linked.In certain embodiments, the polymer is derivatized. For example, freehydroxyl groups may be further modified by reaction with a suitableelectrophile (e.g., anhydride, ester, acrylate, methacrylate). Thematerials prepared from the polyol-based polymers may be hydrogels orelastomers.

DEFINITIONS Chemical Terminology

Definitions of specific functional groups and chemical terms aredescribed in more detail below. For purposes of this invention, thechemical elements are identified in accordance with the Periodic Tableof the Elements, CAS version, Handbook of Chemistry and Physics, 75^(th)Ed., inside cover, and specific functional groups are generally definedas described therein. Additionally, general principles of organicchemistry, as well as specific functional moieties and reactivity, aredescribed in Organic Chemistry, Thomas Sorrell, University ScienceBooks, Sausalito, 1999; Smith and March March's Advanced OrganicChemistry, 5^(th) Edition, John Wiley & Sons, Inc., New York, 2001;Larock, Comprehensive Organic Transformations, VCH Publishers, Inc., NewYork, 1989; Carruthers, Some Modern Methods of Organic Synthesis, 3^(rd)Edition, Cambridge University Press, Cambridge, 1987; the entirecontents of each of which are incorporated herein by reference.

The inventive polymers of the present invention may exist in particulargeometric or stereoisomeric forms. The present invention contemplatesall such polymers, including cis- and trans-isomers, R- andS-enantiomers, diastereomers, (D)-isomers, (L)-isomers, the racemicmixtures thereof, and other mixtures thereof, as falling within thescope of the invention.

Where an isomer/enantiomer is preferred, it may, in some embodiments beprovided substantially free of the corresponding enantiomer, and mayalso be referred to as “optically enriched.” “Optically-enriched,” asused herein, means that the inventive polymer, or polyol orpolycarboxylic acid used to make the inventive polymer, is made up of asignificantly greater proportion of one enantiomer. In certainembodiments the inventive polymer, or polyol or polycarboxylic acid, ismade up of at least about 90% by weight of a preferred enantiomer. Inother embodiments the inventive polymer, or polyol or polycarboxylicacid, is made up of at least about 95%, 98%, or 99% by weight of apreferred enantiomer. Preferred enantiomers may be isolated from racemicmixtures by any method known to those skilled in the art, includingchiral high pressure liquid chromatography (HPLC) and the formation andcrystallization of chiral salts or prepared by asymmetric syntheses.See, for example, Jacques, et al., Enantiomers, Racemates andResolutions (Wiley Interscience, New York, 1981); Wilen, S. H., et al.,Tetrahedron 33:2725 (1977); Eliel, E. L. Stereochemistry of CarbonCompounds (McGraw-Hill, NY, 1962); Wilen, S. H. Tables of ResolvingAgents and Optical Resolutions, p. 268 (E. L. Eliel, Ed., Univ. of NotreDame Press, Notre Dame, Ind. 1972).

It will be appreciated that the inventive polymer, or polyol orpolycarboxylic acid used to make the inventive polymer, as describedherein, may be substituted with any number of substituents or functionalmoieties. In general, the term “substituted” whether preceded by theterm “optionally” or not, and substituents contained in formulas of thisinvention, refer to the replacement of hydrogen radicals in a givenstructure with the radical of a specified substituent. When more thanone position in any given structure may be substituted with more thanone substituent selected from a specified group, the substituent may beeither the same or different at every position. As used herein, the term“substituted” is contemplated to include all permissible substituents oforganic compounds. In a broad aspect, the permissible substituentsinclude acyclic and cyclic, branched and unbranched, carbocyclic andheterocyclic, aromatic and nonaromatic substituents of organiccompounds. For purposes of this invention, heteroatoms such as nitrogenmay have hydrogen substituents and/or any permissible substituents oforganic compounds described herein which satisfy the valencies of theheteroatoms. Furthermore, this invention is not intended to be limitedin any manner by the permissible substituents of organic compounds.

In certain aspects, the term “substituted” is also contemplated toinclude substitution with a “biologically-active agent,” or substitutionwith another inventive polymer, as defined herein.

The term “aliphatic,” as used herein, includes both saturated andunsaturated, nonaromatic, straight chain (i.e., unbranched), branched,acyclic, cyclic (i.e., carbocyclic), or polycyclic hydrocarbons, whichare optionally substituted with one or more functional groups. As willbe appreciated by one of ordinary skill in the art, “aliphatic” isintended herein to include, but is not limited to, alkyl, alkenyl,alkynyl, cycloalkyl, cycloalkenyl, and cycloalkynyl moieties. Thus, asused herein, the term “alkyl” includes straight, branched and cyclicalkyl groups. An analogous convention applies to other generic termssuch as “alkenyl”, “alkynyl”, and the like. Furthermore, as used herein,the terms “alkyl”, “alkenyl”, “alkynyl”, and the like encompass bothsubstituted and unsubstituted groups. In certain embodiments, as usedherein, “aliphatic” is used to indicate those aliphatic groups (cyclic,acyclic, substituted, unsubstituted, branched or unbranched) having 1-20carbon atoms. Aliphatic group substituents include, but are not limitedto, any of the substituents described herein, that result in theformation of a stable moiety (for example, an aliphatic groupsubstituted with one or more aliphatic, alkyl, alkenyl, alkynyl,heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, sulfinyl,sulfonyl, oxo, imino, thiooxo, phosphino, cyano, amino, azido, nitro,hydroxy, thio, and/or halo groups).

The term “stable moiety,” as used herein, preferably refers to a moietywhich possess stability sufficient to allow manufacture, and whichmaintains its integrity for a sufficient period of time to be useful forthe purposes detailed herein.

The term “heteroaliphatic,” as used herein, refers to an aliphaticmoiety, as defined herein, that contain one or more oxygen, sulfur,nitrogen, phosphorus, or silicon atoms, e.g., in place of carbon atoms.In certain embodiments, heteroaliphatic moieties are substituted byindependent replacement of one or more of the hydrogen atoms thereonwith one or more substituents. Heteroaliphatic group substituentsinclude, but are not limited to, any of the substituents describedherein, that result in the formation of a stable moiety (for example, aheteroaliphatic group substituted with one or more aliphatic, alkyl,alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl,sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino, azido, nitro,hydroxy, thio, and/or halo groups).

The term “alkyl,” as used herein, refers to saturated, straight- orbranched-chain hydrocarbon radicals derived from a hydrocarbon moietycontaining between one and twenty carbon atoms by removal of a singlehydrogen atom. In some embodiments, the alkyl group employed in theinvention contains 1-20 carbon atoms. In another embodiment, the alkylgroup employed contains 1-12 carbon atoms. In still other embodiments,the alkyl group contains 1-6 carbon atoms. In yet another embodiments,the alkyl group contains 1-4 carbons. Examples of alkyl radicalsinclude, but are not limited to, methyl, ethyl, n-propyl, isopropyl,n-butyl, iso-butyl, sec-butyl, sec-pentyl, iso-pentyl, tert-butyl,n-pentyl, neopentyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, n-decyl,n-undecyl, dodecyl, and the like, which may bear one or moresubstitutents. Alkyl group substituents include, but are not limited to,any of the substituents described herein, that result in the formationof a stable moiety (for example, an alkyl group substituted with one ormore aliphatic, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl,sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino, azido, nitro,hydroxy, thio, and/or halo groups).

The term “alkenyl,” as used herein, denotes a monovalent group derivedfrom a straight- or branched-chain hydrocarbon moiety having at leastone carbon-carbon double bond by the removal of a single hydrogen atom.In certain embodiments, the alkenyl group employed in the inventioncontains 2-20 carbon atoms. In some embodiments, the alkenyl groupemployed in the invention contains 2-10 carbon atoms. In anotherembodiment, the alkenyl group employed contains 2-8 carbon atoms. Instill other embodiments, the alkenyl group contains 2-6 carbon atoms. Inyet another embodiments, the alkenyl group contains 2-4 carbons. Alkenylgroups include, for example, ethenyl, propenyl, butenyl,1-methyl-2-buten-1-yl, and the like, which may bear one or moresubstituents. Alkenyl group substituents include, but are not limitedto, any of the substituents described herein, that result in theformation of a stable moiety (for example, an alkenyl group substitutedwith one or more aliphatic, heteroaliphatic, heterocyclic, aryl,heteroaryl, acyl, sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino,azido, nitro, hydroxy, thio, and/or halo groups).

The term “alkynyl,” as used herein, refers to a monovalent group derivedfrom a straight- or branched-chain hydrocarbon having at least onecarbon-carbon triple bond by the removal of a single hydrogen atom. Incertain embodiments, the alkynyl group employed in the inventioncontains 2-20 carbon atoms. In some embodiments, the alkynyl groupemployed in the invention contains 2-10 carbon atoms. In anotherembodiment, the alkynyl group employed contains 2-8 carbon atoms. Instill other embodiments, the alkynyl group contains 2-6 carbon atoms. Instill other embodiments, the alkynyl group contains 2-4 carbon atoms.Representative alkynyl groups include, but are not limited to, ethynyl,2-propynyl(propargyl), 1-propynyl, and the like, which may bear one ormore substituents. Alkynyl group substituents include, but are notlimited to, any of the substituents described herein, that result in theformation of a stable moiety (for example, an alkynyl group substitutedwith one or more aliphatic, heteroaliphatic, heterocyclic, aryl,heteroaryl, acyl, sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino,azido, nitro, hydroxy, thio, and/or halo groups).

The term “alkylene,” as used herein, refers to a fully saturatedstraight- or branched-chain alkyl biradical containing between one andtwenty carbon atoms by removal of two hydrogen atoms (the term alkyl isdefined herein). In certain embodiments, an alkylene group issubstituted by independent replacement of one or more of the hydrogenatoms thereon with one or more substituents. Alkylene group substituentsinclude but are not limited to any of the substituents described hereinthat result in the formation of a stable moiety (such as, for example,an alkylene group substituted with one or more aliphatic,heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, sulfinyl,sulfonyl, cyano, amino, azido, nitro, hydroxyl, thiol, and/or halogroups).

The term “alkenylene,” as used herein, refers to a straight- orbranched-chain alkenyl biradical containing between two and twentycarbon atoms by removal of two hydrogen atoms (the term alkenyl isdefined herein). In certain embodiments, an alkenylene group issubstituted by independent replacement of one or more of the hydrogenatoms thereon with one or more substituents. Alkenylene groupsubstituents include but are not limited to any of the substituentsdescribed herein that result in the formation of a stable moiety (suchas, for example, an alkenylene group substituted with one or morealiphatic, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl,sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino, azido, nitro,hydroxyl, thiol, and/or halo groups).

The term “alkynylene” as used herein, refers to a straight- orbranched-chain alkynyl biradical containing between two and twentycarbon atoms by removal of two hydrogen atoms (the term alkynyl isdefined herein). In certain embodiments, an alkynylene group issubstituted by independent replacement of one or more of the hydrogenatoms thereon with one or more substituents. Alkynylene groupsubstituents include but are not limited to any of the substituentsdescribed herein that result in the formation of a stable moiety (suchas, for example, an alkynylene group substituted with one or morealiphatic, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl,sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino, azido, nitro,hydroxyl, thiol, and/or halo groups).

The term “heteroalkylene,” as used herein, refers to an alkylene group,as defined herein, that contains one or more oxygen, sulfur, nitrogen,phosphorus, or silicon atoms, e.g., in place of carbon atoms.

The term “heteroalkenylene,” as used herein, refers to an alkenylenegroup, as defined herein, that contains one or more oxygen, sulfur,nitrogen, phosphorus, or silicon atoms, e.g., in place of carbon atoms.

The term “heteroalkynylene,” as used herein, refers to an alkynylenegroup, as defined herein, that contains one or more oxygen, sulfur,nitrogen, phosphorus, or silicon atoms, e.g., in place of carbon atoms.

The term “heterocyclic,” or “heterocyclyl,” as used herein, refers to annon-aromatic, partially unsaturated or fully saturated, 3- to10-membered ring system, which includes single rings of 3 to 8 atoms insize, and bi- and tri-cyclic ring systems which may include aromaticfive- or six-membered aryl or heteroaryl groups fused to a non-aromaticring. These heterocyclic rings include those having from one to threeheteroatoms independently selected from oxygen, sulfur, and nitrogen, inwhich the nitrogen and sulfur heteroatoms may optionally be oxidized andthe nitrogen heteroatom may optionally be quaternized. In certainembodiments, the term heterocylic refers to a non-aromatic 5-, 6-, or7-membered ring or polycyclic group wherein at least one ring atom is aheteroatom selected from O, S, and N (wherein the nitrogen and sulfurheteroatoms may be optionally oxidized), and the remaining ring atomsare carbon, the radical being joined to the rest of the molecule via anyof the ring atoms. Heterocycyl groups include, but are not limited to, abi- or tri-cyclic group, comprising fused five, six, or seven-memberedrings having between one and three heteroatoms independently selectedfrom the oxygen, sulfur, and nitrogen, wherein (i) each 5-membered ringhas 0 to 2 double bonds, each 6-membered ring has 0 to 2 double bonds,and each 7-membered ring has 0 to 3 double bonds, (ii) the nitrogen andsulfur heteroatoms may be optionally oxidized, (iii) the nitrogenheteroatom may optionally be quaternized, and (iv) any of the aboveheterocyclic rings may be fused to an aryl or heteroaryl ring. Exemplaryheterocycles include azacyclopropanyl, azacyclobutanyl,1,3-diazatidinyl, piperidinyl, piperazinyl, azocanyl, thiaranyl,thietanyl, tetrahydrothiophenyl, dithiolanyl, thiacyclohexanyl,oxiranyl, oxetanyl, tetrahydrofuranyl, tetrahydropuranyl, dioxanyl,oxathiolanyl, morpholinyl, thioxanyl, tetrahydronaphthyl, and the like,which may bear one or more substituents. Substituents include, but arenot limited to, any of the substituents described herein, that result inthe formation of a stable moiety (for example, a heterocyclic groupsubstituted with one or more aliphatic, heteroaliphatic, heterocyclic,aryl, heteroaryl, acyl, sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano,amino, azido, nitro, hydroxy, thio, and/or halo groups).

The term “aryl,” as used herein, refer to stable aromatic mono- orpolycyclic ring system having 3-20 ring atoms, of which all the ringatoms are carbon, and which may be substituted or unsubstituted. Incertain embodiments of the present invention, “aryl” refers to a mono,bi, or tricyclic C₄-C₂₀ aromatic ring system having one, two, or threearomatic rings which include, but not limited to, phenyl, biphenyl,naphthyl, and the like, which may bear one or more substituents. Arylsubstituents include, but are not limited to, any of the substituentsdescribed herein, that result in the formation of a stable moiety (forexample, an aryl group substituted with one or more aliphatic,heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl, sulfinyl,sulfonyl, oxo, imino, thiooxo, cyano, amino, azido, nitro, hydroxy,thio, and/or halo groups).

The term “heteroaryl,” as used herein, refer to stable aromatic mono- orpolycyclic ring system having 3-20 ring atoms, of which one ring atom isselected from S, O, and N; zero, one, or two ring atoms are additionalheteroatoms independently selected from S, O, and N; and the remainingring atoms are carbon, the radical being joined to the rest of themolecule via any of the ring atoms. Exemplary heteroaryls include, butare not limited to pyrrolyl, pyrazolyl, imidazolyl, pyridinyl,pyrimidinyl, pyrazinyl, pyridazinyl, triazinyl, tetrazinyl,pyrrolizinyl, indolyl, quinolinyl, isoquinolinyl, benzoimidazolyl,indazolyl, quinolinyl, isoquinolinyl, quinolizinyl, cinnolinyl,quinazolinyl, phthalazinyl, naphthridinyl, quinoxalinyl, thiophenyl,thianaphthenyl, furanyl, benzofuranyl, benzothiazolyl, thiazolynyl,isothiazolyl, thiadiazolynyl, oxazolyl, isoxazolyl, oxadiaziolyl,oxadiaziolyl, and the like, which may bear one or more substituents.Heteroaryl substituents include, but are not limited to, any of thesubstituents described herein, that result in the formation of a stablemoiety (for example, a heteroaryl group substituted with one or morealiphatic, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl,sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino, azido, nitro,hydroxy, thio, and/or halo groups).

The term “acyl,” as used herein, refers to a group having the generalformula —C(═O)R, where R is hydrogen, halogen, hydroxyl, thiol,optionally substituted amino, optionally substituted hydrazino,optionally substituted aliphatic, optionally substitutedheteroaliphatic, optionally substituted alkyl, optionally substitutedalkenyl, optionally substituted alkynyl, optionally substituted aryl,alkyloxy, alkylthioxy, alkylamino, dialkylamino, arylamino, diarylamino,optionally substituted aryl, optionally substituted heteroaryl, oroptionally substituted heterocycyl. Exemplary acyl groups includealdehydes (—CHO), carboxylic acids (—CO₂H), ketones (such as an acetylgroup [—(C═O)CH₃], esters, amides, carbonates, carbamates, and ureas.Acyl substituents include, but are not limited to, any of thesubstituents described herein, that result in the formation of a stablemoiety (for example, a heteroaryl group substituted with one or morealiphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl,heteroaryl, acyl, sulfinyl, sulfonyl, oxo, imino, thiooxo, cyano, amino,azido, nitro, hydroxy, thio, and/or halo groups).

A “suitable carboxylic acid protecting group,” or “protected carboxylicacid,” as used herein, are well known in the art and include thosedescribed in detail in Greene (1999). Examples of suitably protectedcarboxylic acids further include, but are not limited to, silyl-,alkyl-, alkenyl-, aryl-, and arylalkyl-protected carboxylic acids.Examples of suitable silyl groups include trimethylsilyl, triethylsilyl,t-butyldimethylsilyl, t-butyldiphenylsilyl, triisopropylsilyl, and thelike. Examples of suitable alkyl groups include methyl, benzyl,p-methoxybenzyl, 3,4-dimethoxybenzyl, trityl, t-butyl,tetrahydropyran-2-yl. Examples of suitable alkenyl groups include allyl.Examples of suitable aryl groups include optionally substituted phenyl,biphenyl, or naphthyl. Examples of suitable arylalkyl groups includeoptionally substituted benzyl (e.g., p-methoxybenzyl (MPM),3,4-dimethoxybenzyl, O-nitrobenzyl, p-nitrobenzyl, p-halobenzyl,2,6-dichlorobenzyl, p-cyanobenzyl), and 2- and 4-picolyl.

An “activated carboxylic acid,” as used herein, includes esters,anhydrides, acyl halides, sulfonylated carboxylic acids (e.g.,—C(O)O-trifluoromethylsulfonyl (—OTf), —C(O)O-tolylsulfonyl (—OTs),—C(O)O-methanesulfonyl (—OMs), —C(O)O-(4-nitrophenylsulfonyl) (—ONos),and —C(O)O-(2-nitrophenylsulfonyl) (—ONs)), and the like.

The term “acylene,” “acyl linkage,” or “bridging acyl linkage,” or“bridging acyl group,” as used herein, refers to an acyl group havingthe general formulae: —R^(a)—(C═X)—R^(a)—, —R^(a)—X²(C═X¹)—R^(a)—, or—R^(a)—X²(C═X¹)X³—R^(a)—, where X¹, X², and X³ is, independently,oxygen, sulfur, or NR^(n), wherein R^(n) is any substitutent, includinghydrogen, which results in a stable moiety, and R^(a) is an optionallysubstituted alkylene, alkenylene, alkynylene, heteroalkylene,heteroalkenylene, or heteroalkynylene group, as defined above andherein. Exemplary bridging acyl groups include—(C═O)—O-(aliphatic)-NR^(n)NR^(n)—(aliphatic)-NR^(n)NR^(n)—(C═O)—;—(C═O)-(aliphatic)-NR^(n)NR^(n)-(aliphatic)-NR^(n)NR^(n)—(C═O)—;-(aliphatic)-(C═O)—O-(aliphatic)-NR^(n)NR^(n)-(aliphatic)-NR^(n)NR^(n)—(C═O)—;-(aliphatic)-(C═O)-(aliphatic)-NR^(n)R^(n)—(aliphatic)-NR^(n)NR^(n)—(C═O)—;-(aliphatic)-O(C═O)-(aliphatic)-; -(aliphatic)-NR^(n)(C═O)-(aliphatic)-;-(aliphatic)-O(C═NR^(n))-(aliphatic)-;-(aliphatic)-NR^(n)(C═NR^(n))-(aliphatic)-;-(aliphatic)-(C═O)-(aliphatic)-; -(aliphatic)-(C═NR^(n))-(aliphatic)-;-(aliphatic)-S(C═S)-(aliphatic)-; -(aliphatic)-NR^(n)(C═S)-(aliphatic)-;-(aliphatic)-S(C═NR^(n))-(aliphatic)-; -(aliphatic)-O(C═S)-(aliphatic)-;-(aliphatic)-(C═S)-(aliphatic)-; or -(aliphatic)-S(C═O)-(aliphatic)-,and the like, which may bear one or more substituents.

The term “arylene,” as used herein refers to an aryl biradical derivedfrom an aryl group by removal of two hydrogen atoms. The term“heteroarylene,” as used herein refers to a heteroaryl biradical derivedfrom a heteroaryl group by removal of two hydrogen atoms. Arylene andheteroarylene groups may be substituted or unsubstituted. Additionally,arylene and heteroarylene groups may be incorporated as a linker groupinto an alkylene, alkenylene, alkynylene, heteroalkylene,heteroalkenylene, or heteroalkynylene group. For example, an arylene orheteroarylene further incorporated into an alkylene group may correspondto the formula —(CH₂)_(c)-(arylene or heteroarylene group)-(CH₂)_(d)—,wherein c and d are, independently, an integer between 0 to 20. Incertain embodiments, c and d are 0. In certain embodiments, c and d are1.

An “acrylate group,” or an “acrylate moiety,” as used herein, is an acylgroup of the formula: —C(═O)C(R^(e))═C(R^(f))₂, wherein R^(e) and R^(f)are, independently, any substituent which results in a stable acrylatemoiety, such as, for example, hydrogen, aliphatic, aryl, heteroaryl,heterocyclyl, or halogen. An “acrylate group,” as defined above,comprises “methacrylate,” wherein R^(e) is —CH₃ and each R^(f) ishydrogen.

The term “sulfinyl,” as used herein, refers to a group of the formulaR^(g)—S(═O)— where there is one double bond between the sulfur andoxygen, and where R^(g) may be an optionally substituted aliphatic,aryl, hydroxy, thiol, amino, aryl, heteroaryl, or heterocyclyl. The term“aliphaticsulfinyl” refers to a sulfinyl group where R^(g) may be anoptionally substituted aliphatic, heterocyclyl, or heteroaliphatic. Theterm “arylsulfinyl” refers to a sulfinyl group where R may be anoptionally substituted aryl or heteroaryl.

The term “sulfonyl,” as used herein, refers to an organic radical (orfunctional group) obtained from an sulfonic acid by the removal of thehydroxyl group. Sulfonyl groups can be written as having the generalformula R^(g)—S(═O)₂—, where there are two double bonds between thesulfur and oxygen, and where R^(g) may be an optionally substitutedaliphatic, heteroaliphatic, aryl, hydroxy, thiol, amino, aryl,heteroaryl, or heterocyclic. The term “aliphaticsulfonyl” refers to asulfonyl group where R^(g) may be an optionally substituted aliphatic,heteroaliphatic, or heterocyclic. The term “alkylsulfonyl” refers to asulfonyl group where R^(g) may be an optionally substituted alkyl. Theterm “arylsulfonyl” refers to a sulfonyl group where R^(g) may be anoptionally substituted aryl or heteroaryl. Exemplary aryl or alkylsulfonyl groups include tosyl (toluene sulfonyl, CH₃C₆H₄SO₂—), mesyl(methyl sulfonyl, CH₃SO₂—), and trifluoromethanesulfonyl (CF₃SO₂—).

The term “amino,” as used herein, refers to a group of the formula(—NH₂). An “optionally substituted amino” refers to a group of theformula (—NR^(h) ₂), wherein R^(h) can be hydrogen, or any substitutent.Substituents include, but are not limited to, any of the substituentsdescribed herein, that result in the formation of a stable moiety (forexample, an amino group substituted with one or more aliphatic, alkyl,alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl, heteroaryl, acyl,sulfinyl, sulfonyl, amino, nitro, hydroxy, and/or thio groups).

A “suitable amino-protecting group,” as used herein, is well known inthe art and include those described in detail in Protecting Groups inOrganic Synthesis, T. W. Greene and P. G. M. Wuts, 3^(rd) edition, JohnWiley & Sons, 1999, the entirety of which is incorporated herein byreference. Suitable amino-protecting groups include methyl carbamate,ethyl carbamate, 9-fluorenylmethyl carbamate (Fmoc),9-(2-sulfo)fluorenylmethyl carbamate, 9-(2,7-dibromo)fluoroenylmethylcarbamate,2,7-di-t-butyl-[9-(10,10-dioxo-10,10,10,10-tetrahydrothioxanthyl)]methylcarbamate (DBD-Tmoc), 4-methoxyphenacyl carbamate (Phenoc),2,2,2-trichloroethyl carbamate (Troc), 2-trimethylsilylethyl carbamate(Teoc), 2-phenylethyl carbamate (hZ), 1-(1-adamantyl)-1-methylethylcarbamate (Adpoc), 1,1-dimethyl-2-haloethyl carbamate,1,1-dimethyl-2,2-dibromoethyl carbamate (DB-t-BOC),1,1-dimethyl-2,2,2-trichloroethyl carbamate (TCBOC),1-methyl-1-(4-biphenylyl)ethyl carbamate (Bpoc),1-(3,5-di-t-butylphenyl)-1-methylethyl carbamate (t-Bumeoc), 2-(2′- and4′-pyridyl)ethyl carbamate (Pyoc), 2-(N,N-dicyclohexylcarboxamido)ethylcarbamate, t-butyl carbamate (BOC), 1-adamantyl carbamate (Adoc), vinylcarbamate (Voc), allyl carbamate (Alloc), 1-isopropylallyl carbamate(Ipaoc), cinnamyl carbamate (Coc), 4-nitrocinnamyl carbamate (Noc),8-quinolyl carbamate, N-hydroxypiperidinyl carbamate, alkyldithiocarbamate, benzyl carbamate (Cbz), p-methoxybenzyl carbamate (Moz),p-nitrobenzyl carbamate, p-bromobenzyl carbamate, p-chlorobenzylcarbamate, 2,4-dichlorobenzyl carbamate, 4-methylsulfinylbenzylcarbamate (Msz), 9-anthrylmethyl carbamate, diphenylmethyl carbamate,2-methylthioethyl carbamate, 2-methylsulfonylethyl carbamate,2-(p-toluenesulfonyl)ethyl carbamate, [2-(1,3-dithianyl)]methylcarbamate (Dmoc), 4-methylthiophenyl carbamate (Mtpc),2,4-dimethylthiophenyl carbamate (Bmpc), 2-phosphonioethyl carbamate(Peoc), 2-triphenylphosphonioisopropyl carbamate (Ppoc),1,1-dimethyl-2-cyanoethyl carbamate, m-chloro-p-acyloxybenzyl carbamate,p-(dihydroxyboryl)benzyl carbamate, 5-benzisoxazolylmethyl carbamate,2-(trifluoromethyl)-6-chromonylmethyl carbamate (Tcroc), m-nitrophenylcarbamate, 3,5-dimethoxybenzyl carbamate, o-nitrobenzyl carbamate,3,4-dimethoxy-6-nitrobenzyl carbamate, phenyl(o-nitrophenyl)methylcarbamate, phenothiazinyl-(10)-carbonyl derivative,N′-p-toluenesulfonylaminocarbonyl derivative, N′-phenylaminothiocarbonylderivative, t-amyl carbamate, S-benzyl thiocarbamate, p-cyanobenzylcarbamate, cyclobutyl carbamate, cyclohexyl carbamate, cyclopentylcarbamate, cyclopropylmethyl carbamate, p-decyloxybenzyl carbamate,2,2-dimethoxycarbonylvinyl carbamate, o-(N,N-dimethylcarboxamido)benzylcarbamate, 1,1-dimethyl-3-(N,N-dimethylcarboxamido)propyl carbamate,1,1-dimethylpropynyl carbamate, di(2-pyridyl)methyl carbamate,2-furanylmethyl carbamate, 2-iodoethyl carbamate, isoborynl carbamate,isobutyl carbamate, isonicotinyl carbamate,p-(p′-methoxyphenylazo)benzyl carbamate, 1-methylcyclobutyl carbamate,1-methylcyclohexyl carbamate, 1-methyl-1-cyclopropylmethyl carbamate,1-methyl-1-(3,5-dimethoxyphenyl)ethyl carbamate,1-methyl-1-(p-phenylazophenyl)ethyl carbamate, 1-methyl-1-phenylethylcarbamate, 1-methyl-1-(4-pyridyl)ethyl carbamate, phenyl carbamate,p-(phenylazo)benzyl carbamate, 2,4,6-tri-t-butylphenyl carbamate,4-(trimethylammonium)benzyl carbamate, 2,4,6-trimethylbenzyl carbamate,formamide, acetamide, chloroacetamide, trichloroacetamide,trifluoroacetamide, phenylacetamide, 3-phenylpropanamide, picolinamide,3-pyridylcarboxamide, N-benzoylphenylalanyl derivative, benzamide,p-phenylbenzamide, o-nitrophenylacetamide, o-nitrophenoxyacetamide,acetoacetamide, (N′-dithiobenzyloxycarbonylamino)acetamide,3-(p-hydroxyphenyl)propanamide, 3-(o-nitrophenyl)propanamide,2-methyl-2-(o-nitrophenoxy)propanamide,2-methyl-2-(o-phenylazophenoxy)propanamide, 4-chlorobutanamide,3-methyl-3-nitrobutanamide, o-nitrocinnamide, N-acetylmethioninederivative, o-nitrobenzamide, o-(benzoyloxymethyl)benzamide,4,5-diphenyl-3-oxazolin-2-one, N-phthalimide, N-dithiasuccinimide (Dts),N-2,3-diphenylmaleimide, N-2,5-dimethylpyrrole,N-1,1,4,4-tetramethyldisilylazacyclopentane adduct (STABASE),5-substituted 1,3-dimethyl-1,3,5-triazacyclohexan-2-one, 5-substituted1,3-dibenzyl-1,3,5-triazacyclohexan-2-one, 1-substituted3,5-dinitro-4-pyridone, N-methylamine, N-allylamine,N-[2-(trimethylsilyl)ethoxy]methylamine (SEM), N-3-acetoxypropylamine,N-(1-isopropyl-4-nitro-2-oxo-3-pyrrolin-3-yl)amine, quaternary ammoniumsalts, N-benzylamine, N-di(4-methoxyphenyl)methylamine,N-5-dibenzosuberylamine, N-triphenylmethylamine (Tr),N-[(4-methoxyphenyl)diphenylmethyl]amine (MMTr),N-9-phenylfluorenylamine (PhF),N-2,7-dichloro-9-fluorenylmethyleneamine, N-ferrocenylmethylamino (Fcm),N-2-picolylamino N′-oxide, N-1,1-dimethylthiomethyleneamine,N-benzylideneamine, N-p-methoxybenzylideneamine,N-diphenylmethyleneamine, N-[(2-pyridyl)mesityl]methyleneamine,N—(N′,N′-dimethylaminomethylene)amine, N,N′-isopropylidenediamine,N-p-nitrobenzylideneamine, N-salicylideneamine,N-5-chlorosalicylideneamine,N-(5-chloro-2-hydroxyphenyl)phenylmethyleneamine,N-cyclohexylideneamine, N-(5,5-dimethyl-3-oxo-1-cyclohexenyl)amine,N-borane derivative, N-diphenylborinic acid derivative,N-[phenyl(pentacarbonylchromium- or tungsten)carbonyl]amine, N-copperchelate, N-zinc chelate, N-nitroamine, N-nitrosoamine, amine N-oxide,diphenylphosphinamide (Dpp), dimethylthiophosphinamide (Mpt),diphenylthiophosphinamide (Ppt), dialkyl phosphoramidates, dibenzylphosphoramidate, diphenyl phosphoramidate, benzenesulfenamide,o-nitrobenzenesulfenamide (Nps), 2,4-dinitrobenzenesulfenamide,pentachlorobenzenesulfenamide, 2-nitro-4-methoxybenzenesulfenamide,triphenylmethylsulfenamide, 3-nitropyridinesulfenamide (Npys),p-toluenesulfonamide (Ts), benzenesulfonamide,2,3,6,-trimethyl-4-methoxybenzenesulfonamide (Mtr),2,4,6-trimethoxybenzenesulfonamide (Mtb),2,6-dimethyl-4-methoxybenzenesulfonamide (Pme),2,3,5,6-tetramethyl-4-methoxybenzenesulfonamide (Mte),4-methoxybenzenesulfonamide (Mbs), 2,4,6-trimethylbenzenesulfonamide(Mts), 2,6-dimethoxy-4-methylbenzenesulfonamide (iMds),2,2,5,7,8-pentamethylchroman-6-sulfonamide (Pmc), methanesulfonamide(Ms), β-trimethylsilylethanesulfonamide (SES), 9-anthracenesulfonamide,4-(4′,8′-dimethoxynaphthylmethyl)benzenesulfonamide (DNMBS),benzylsulfonamide, trifluoromethylsulfonamide, and phenacylsulfonamide.

The term “hydroxy,” or “hydroxyl,” as used herein, refers to a group ofthe formula (—OH). An “optionally substituted hydroxy” refers to a groupof the formula (—OR^(i)), wherein R^(i) can be hydrogen, or anysubstitutent which results in a stable moiety (for example, a hydroxygroup substituted with a suitable hydroxyl protecting group, analiphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl,heteroaryl, acyl, sulfinyl, and/or sulfonyl group).

An “activated” hydroxyl group, as used herein, includes sulfonyl groups(e.g., O-trifluoromethylsulfonyl (—OTf), O-tolylsulfonyl (—OTs),O-methanesulfonyl (—OMs), O-(4-nitrophenylsulfonyl) (—ONos), andO-(2-nitrophenylsulfonyl) (—ONs)), and acyl groups.

A “suitable hydroxyl protecting group” as used herein, is well known inthe art and include those described in detail in Protecting Groups inOrganic Synthesis, T. W. Greene and P. G. M. Wuts, 3^(rd) edition, JohnWiley & Sons, 1999, the entirety of which is incorporated herein byreference. Suitable hydroxyl protecting groups include methyl,methoxylmethyl (MOM), methylthiomethyl (MTM), t-butylthiomethyl,(phenyldimethylsilyl)methoxymethyl (SMOM), benzyloxymethyl (BOM),p-methoxybenzyloxymethyl (PMBM), (4-methoxyphenoxy)methyl (p-AOM),guaiacolmethyl (GUM), t-butoxymethyl, 4-pentenyloxymethyl (POM),siloxymethyl, 2-methoxyethoxymethyl (MEM), 2,2,2-trichloroethoxymethyl,bis(2-chloroethoxy)methyl, 2-(trimethylsilyl)ethoxymethyl (SEMOR),tetrahydropyranyl (THP), 3-bromotetrahydropyranyl,tetrahydrothiopyranyl, 1-methoxycyclohexyl, 4-methoxytetrahydropyranyl(MTHP), 4-methoxytetrahydrothiopyranyl, 4-methoxytetrahydrothiopyranylS,S-dioxide, 1-[(2-chloro-4-methyl)phenyl]-4-methoxypiperidin-4-yl(CTMP), 1,4-dioxan-2-yl, tetrahydrofuranyl, tetrahydrothiofuranyl,2,3,3a,4,5,6,7,7a-octahydro-7,8,8-trimethyl-4,7-methanobenzofuran-2-yl,1-ethoxyethyl, 1-(2-chloroethoxy)ethyl, 1-methyl-1-methoxyethyl,1-methyl-1-benzyloxyethyl, 1-methyl-1-benzyloxy-2-fluoroethyl,2,2,2-trichloroethyl, 2-trimethylsilylethyl, 2-(phenylselenyl)ethyl,t-butyl, allyl, p-chlorophenyl, p-methoxyphenyl, 2,4-dinitrophenyl,benzyl, p-methoxybenzyl, 3,4-dimethoxybenzyl, o-nitrobenzyl,p-nitrobenzyl, p-halobenzyl, 2,6-dichlorobenzyl, p-cyanobenzyl,p-phenylbenzyl, 2-picolyl, 4-picolyl, 3-methyl-2-picolyl N-oxido,diphenylmethyl, p,p′-dinitrobenzhydryl, 5-dibenzosuberyl,triphenylmethyl, α-naphthyldiphenylmethyl,p-methoxyphenyldiphenylmethyl, di(p-methoxyphenyl)phenylmethyl,tri(p-methoxyphenyl)methyl, 4-(4′-bromophenacyloxyphenyl)diphenylmethyl,4,4′,4″-tris(4,5-dichlorophthalimidophenyl)methyl,4,4′,4″-tris(levulinoyloxyphenyl)methyl,4,4′,4″-tris(benzoyloxyphenyl)methyl,3-(imidazol-1-yl)bis(4′,4″-dimethoxyphenyl)methyl,1,1-bis(4-methoxyphenyl)-1′-pyrenylmethyl, 9-anthryl,9-(9-phenyl)xanthenyl, 9-(9-phenyl-10-oxo)anthryl,1,3-benzodithiolan-2-yl, benzisothiazolyl S,S-dioxido, trimethylsilyl(TMS), triethylsilyl (TES), triisopropylsilyl (TIPS),dimethylisopropylsilyl (IPDMS), diethylisopropylsilyl (DEIPS),dimethylthexylsilyl, t-butyldimethylsilyl (TBDMS), t-butyldiphenylsilyl(TBDPS), tribenzylsilyl, tri-p-xylylsilyl, triphenylsilyl,diphenylmethylsilyl (DPMS), t-butylmethoxyphenylsilyl (TBMPS), formate,benzoylformate, acetate, chloroacetate, dichloroacetate,trichloroacetate, trifluoroacetate, methoxyacetate,triphenylmethoxyacetate, phenoxyacetate, p-chlorophenoxyacetate,3-phenylpropionate, 4-oxopentanoate (levulinate),4,4-(ethylenedithio)pentanoate (levulinoyldithioacetal), pivaloate,adamantoate, crotonate, 4-methoxycrotonate, benzoate, p-phenylbenzoate,2,4,6-trimethylbenzoate (mesitoate), alkyl methyl carbonate,9-fluorenylmethyl carbonate (Fmoc), alkyl ethyl carbonate, alkyl2,2,2-trichloroethyl carbonate (Troc), 2-(trimethylsilyl)ethyl carbonate(TMSEC), 2-(phenylsulfonyl)ethyl carbonate (Psec),2-(triphenylphosphonio) ethyl carbonate (Peoc), alkyl isobutylcarbonate, alkyl vinyl carbonate alkyl allyl carbonate, alkylp-nitrophenyl carbonate, alkyl benzyl carbonate, alkyl p-methoxybenzylcarbonate, alkyl 3,4-dimethoxybenzyl carbonate, alkyl o-nitrobenzylcarbonate, alkyl p-nitrobenzyl carbonate, alkyl S-benzyl thiocarbonate,4-ethoxy-1-napththyl carbonate, methyl dithiocarbonate, 2-iodobenzoate,4-azidobutyrate, 4-nitro-4-methylpentanoate, o-(dibromomethyl)benzoate,2-formylbenzenesulfonate, 2-(methylthiomethoxy)ethyl,4-(methylthiomethoxy)butyrate, 2-(methylthiomethoxymethyl)benzoate,2,6-dichloro-4-methylphenoxyacetate,2,6-dichloro-4-(1,1,3,3-tetramethylbutyl)phenoxyacetate,2,4-bis(1,1-dimethylpropyl)phenoxyacetate, chlorodiphenylacetate,isobutyrate, monosuccinoate, (E)-2-methyl-2-butenoate,o-(methoxycarbonyl)benzoate, α-naphthoate, nitrate, alkylN,N,N′,N′-tetramethylphosphorodiamidate, alkyl N-phenylcarbamate,borate, dimethylphosphinothioyl, alkyl 2,4-dinitrophenylsulfenate,sulfate, methanesulfonate (mesylate), benzylsulfonate, and tosylate(Ts). For protecting 1,2- or 1,3-diols, the protecting groups includemethylene acetal, ethylidene acetal, 1-t-butylethylidene ketal,1-phenylethylidene ketal, (4-methoxyphenyl)ethylidene acetal,2,2,2-trichloroethylidene acetal, acetonide, cyclopentylidene ketal,cyclohexylidene ketal, cycloheptylidene ketal, benzylidene acetal,p-methoxybenzylidene acetal, 2,4-dimethoxybenzylidene ketal,3,4-dimethoxybenzylidene acetal, 2-nitrobenzylidene acetal,methoxymethylene acetal, ethoxymethylene acetal, dimethoxymethyleneortho ester, 1-methoxyethylidene ortho ester, 1-ethoxyethylidine orthoester, 1,2-dimethoxyethylidene ortho ester, α-methoxybenzylidene orthoester, 1-(N,N-dimethylamino)ethylidene derivative,α-(N,N′-dimethylamino)benzylidene derivative, 2-oxacyclopentylideneortho ester, di-t-butylsilylene group (DTBS),1,3-(1,1,3,3-tetraisopropyldisiloxanylidene) derivative (TIPDS),tetra-t-butoxydisiloxane-1,3-diylidene derivative (TBDS), cycliccarbonates, cyclic boronates, ethyl boronate, and phenyl boronate.

The term “thio,” or “thiol,” as used herein, refers to a group of theformula (—SH). An “optionally substituted thiol” refers to a group ofthe formula (—SR^(r)), wherein R^(r) can be hydrogen, or anysubstitutent. Substituents include, but are not limited to, any of thesubstituents described herein, that result in the formation of a stablemoiety (for example, a thio group substituted with one or morealiphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl,heteroaryl, acyl, sulfinyl, and/or sulfonyl).

A “suitable thiol protecting group,” as used herein, are well known inthe art and include those described in detail in Protecting Groups inOrganic Synthesis, T. W. Greene and P. G. M. Wuts, 3^(rd) edition, JohnWiley & Sons, 1999, the entirety of which is incorporated herein byreference. Examples of suitably protected thiol groups further include,but are not limited to, thioesters, carbonates, sulfonates allylthioethers, thioethers, silyl thioethers, alkyl thioethers, arylalkylthioethers, and alkoxyalkyl thioethers. Examples of suitable estergroups include formates, acetates, proprionates, pentanoates,crotonates, and benzoates. Specific examples of suitable ester groupsinclude formate, benzoyl formate, chloroacetate, trifluoroacetate,methoxyacetate, triphenylmethoxyacetate, p-chlorophenoxyacetate,3-phenylpropionate, 4-oxopentanoate, 4,4-(ethylenedithio)pentanoate,pivaloate (trimethylacetate), crotonate, 4-methoxy-crotonate, benzoate,p-benzylbenzoate, 2,4,6-trimethylbenzoate. Examples of suitablecarbonates include 9-fluorenylmethyl, ethyl, 2,2,2-trichloroethyl,2-(trimethylsilyl)ethyl, 2-(phenylsulfonyl)ethyl, vinyl, allyl, andp-nitrobenzyl carbonate. Examples of suitable silyl groups includetrimethylsilyl, triethylsilyl, t-butyldimethylsilyl,t-butyldiphenylsilyl, triisopropylsilyl ether, and other trialkylsilylethers. Examples of suitable alkyl groups include methyl, benzyl,p-methoxybenzyl, 3,4-dimethoxybenzyl, trityl, t-butyl, and allyl ether,or derivatives thereof. Examples of suitable arylalkyl groups includebenzyl, p-methoxybenzyl (MPM), 3,4-dimethoxybenzyl, O-nitrobenzyl,p-nitrobenzyl, p-halobenzyl, 2,6-dichlorobenzyl, p-cyanobenzyl, 2- and4-picolyl ethers.

The terms “halo” and “halogen” as used herein refer to an atom selectedfrom fluorine (fluoro, —F), chlorine (chloro, —Cl), bromine (bromo,—Br), and iodine (iodo, —I).

The term “cyano,” as used herein, refers to a group of the formula(—CN).

The term “isocyano,” as used herein, refers to a group of the formula(—NC).

The term “azido,” as used herein, refers to a group of the formula(—N₃). An “optionally substituted azido” refers to a group of theformula (—N₃R^(i)), wherein R^(i) can be any substitutent (other thanhydrogen). Substituents include, but are not limited to, any of thesubstituents described herein, that result in the formation of a stablemoiety (for example, an azido group substituted with one or morealiphatic, alkyl, alkenyl, alkynyl, heteroaliphatic, heterocyclic, aryl,heteroaryl, acyl, sulfinyl, and/or sulfonyl groups).

The term “hydrazine” or “hydrazino,” as used herein, refers to the groupof the formula —N(R^(j))N(R^(j))₂, wherein R^(j) can be anysubstitutent. Substituents include, but are not limited to, any of thesubstituents described herein, that result in the formation of a stablemoiety (for example, an hydrazino group substituted with one or morehydrogens, aliphatic, alkyl, alkenyl, alkynyl, heteroaliphatic,heterocyclic, aryl, heteroaryl, acyl, sulfinyl, and/or sulfonyl groups).

The term “nitro,” as used herein, refers to a group of the formula(—NO₂).

The term “oxo,” as used herein, refers to a group of the formula (═O).

The term “thiooxo,” as used herein, refers to a group of the formula(═S).

The term “imino,” as used herein, refers to a group of the formula(═NR^(r)), wherein R^(r) corresponds to hydrogen or any substitutent asdescribed herein, that results in the formation of a stable moiety (forexample, a suitable amino protecting group; substituted or unsubstitutedamino; acyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkenyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkynyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkyl; cyclicor acylic, branched or unbranched, substituted or unsubstitutedheteroalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkynyl; substituted or unsubstituted aryl; orsubstituted or unsubstituted heteroaryl).

The following definitions are more general terms used throughout thepresent application:

The term “subject,” as used herein, refers to any animal. In certainembodiments, the subject is a mammal. In certain embodiments, the term“subject”, as used herein, refers to a human (e.g., a man, a woman, or achild).

The terms “administer,” “administering,” or “administration,” as usedherein refers to implanting, absorbing, ingesting, injecting, orinhaling, the inventive polymer or compound.

The terms “treat” or “treating,” as used herein, refers to partially orcompletely alleviating, inhibiting, ameliorating, and/or relieving thedisease or condition from which the subject is suffering.

The terms “effective amount” and “therapeutically effective amount,” asused herein, refer to the amount or concentration of a biologicallyactive agent conjugated to an inventive polymer of the presently claimedinvention, or amount or concentration of an inventive polymer, that,when administered to a subject, is effective to at least partially treata condition from which the subject is suffering.

As used herein, when two entities are “conjugated” to one another theyare linked by a direct or indirect covalent or non-covalent interaction.In certain embodiments, the association is covalent. In otherembodiments, the association is non-covalent. Non-covalent interactionsinclude hydrogen bonding, van der Waals interactions, hydrophobicinteractions, magnetic interactions, electrostatic interactions, etc. Anindirect covalent interaction is when two entities are covalentlyconnected through a linker group.

“Biocompatible”: The term “biocompatible”, as used herein is intended todescribe inventive polymers that do not elicit a substantial detrimentalresponse in vivo. In certain embodiments, the inventive polymers are“biocompatible” if they are not toxic to cells. In certain embodiments,the inventive polymers are “biocompatible” if their addition to cells invitro results in less than or equal to 20% cell death, and/or theiradministration in vivo does not induce inflammation or other suchadverse effects. In certain embodiments, biocompatible polymers are alsobiodegradable.

“Biodegradable”: As used herein, “biodegradable” inventive polymers arethose that, when introduced into cells, are broken down by the cellularmachinery (e.g., enzymatic degradation) or by hydrolysis into componentsthat the cells can either reuse or dispose of without significant toxiceffects on the cells. In certain embodiments, the components do notinduce inflammation and/or other adverse effects in vivo. In certainembodiments, the chemical reactions relied upon to break down thebiodegradable inventive polymers are enzymatically broken down. Forexample, the inventive polymers may be broken down in part by thehydrolysis of ester bonds. In certain embodiments, biodegradablepolymers are polymers that fully degrade down to their monomericcomponents under physiological conditions. In certain embodiments,biodegradable polymers are also biocompatible.

The term “pharmaceutically acceptable salt” includes acid additionsalts, that is salts derived from treating a compound of the presentlyclaimed invention with an organic or inorganic acid such as, forexample, acetic, lactic, citric, cinnamic, tartaric, succinic, fumaric,maleic, malonic, mandelic, malic, oxalic, propionic, hydrochloric,hydrobromic, phosphoric, nitric, sulfuric, glycolic, pyruvic,methanesulfonic, ethanesulfonic, toluenesulfonic, salicylic, benzoic, orsimilarly known acceptable acids. Where a compound the presently claimedinvention contains a substituent with acidic properties, for instance, acarboxylic acid, the term also includes salts derived from bases, forexample, sodium, potassium, calcium, magnesium, lithium, and bariumsalts.

The term “hydrogel,” as used herein, is a polymer which absorbs at least10 wt % of water (in the presence of an abundance of water). When thecontent of water exceeds 95% of the total weight (i.e., 95 wt %), thehydrogel is a superabsorbent hydrogel.

The term “elastomer,” as used herein, is a polymer that can returnrapidly to the approximate shape from which it has been substantiallydistorted by a weak stress. In certain embodiments, the elastomer can bestretched repeatedly to at least twice its original length and which,upon release of the stress, will immediately return to approximately itsoriginal length. In certain embodiments, the elastomer polymer does notsustain permanent structural deformation upon stretching the elastomerpolymer between about 1% to 300% its original length.

As used herein, the term “substantially clear,” or “clear,” “opticallyclear,” or “transparent,” refers to a sample specimen with a lighttransmission percentage of at least 85%, at least 90%, at least 95%, orat least 99%. It is possible to measure the degree of light transmissionusing ASTM D-1003 (Standard Test Method for Haze and LuminousTransmittance of Transparent Plastics), and this test method is used toevaluate light transmission and scattering of transparent plastics for adefined specimen thickness. The term “substantially clear,” or “clear,”“optically clear,” or “transparent,” may also refer to a sample specimenwhich has a constant refractive index through the sample in the viewingdirection. The perceived transparency or optical clarity is dependent onthe thickness of the sample used for assessment, and the optical claritywill decrease with increasing thickness. Any areas of opaque material(such as colorants) or areas of different refractive index, will resultin a loss of optical clarity due to refraction and scattering. Opticalclarity is also dependent on surface reflections from the sample.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Schematic representation of the general synthetic scheme ofxylitol-based polymers. Xylitol (1), was polymerized with citric acid(2) or sebacic acid (3) into poly(xylitol-co-citrate) (PXC) (4), andpoly(xylitol-co-sebacate) (PXS) (5). Further polycondensation of PXSyielded elastomers. Photo-crosslinkable hydrogels were obtained byacrylation of PXC in ddH₂O using methacrylic anhydride (6) to yieldPXC-methacrylate (PXCma) (7). PXCma was polymerized into a hydrogel byfree radical polymerization using a photoinitiator. A simplifiedrepresentation of the polymers is shown. R can be H, OCH₂(CH(OR))₃CH₂OR(xylitol), —CO(CH₂)₆COOR (sebacic acid), CO(CH₂)ROC(COOR)(CH₂)COOR(citric acid), or —C(CH₃)═CH₂ (methacrylate group).

FIG. 2. (A) FTIR analysis of xylitol-based polymers. (B) Typical tensilestress versus strain curve of the PXS elastomers. (C) Typicalcompression stress versus strain plot of the 10% w/v PXCma hydrogel,with cyclic compression at 40, 50, 75%, to failure (at ˜80%). (D) Invivo mass loss over time.

FIG. 3. (A) Phase contrast images (10×) of human primary fibroblastsafter 5 days of in vitro culture, seeded on PLGA (i), PXS 1:1 (ii) andPXS 1:2 (iii). Bars represent 250 μm. (B) Growth rates of fibroblasts onPLGA, PXS 1:1 and PXS 1:2, expressed as cell differential. (C) MTT assayof fibroblasts exposed to different PXCma pre-polymer fractions in theirgrowth medium. (D) Representative images of H&E stained sections ofsubcutaneous implantation sites of (i) PLGA discs, (ii) PXS 1:1 discs,(iii) PXS 1:2 discs, (iv) 10% w/v PXCma hydrogel discs, 1 week afterimplantation. (v) Shows PXS 1:1 implantation site at week 5 (˜73% haddegraded), and (vi) shows PXS 1:2 at week 12 (no degradation). The arrow(i) points to a vessel of the fibrous capsule surrounding the PLGAimplant where some perivascular infiltration is observed. P=polymer,FC=fibrous capsule, M=muscle. Inserts are 5× overviews, full images aremagnified 25×. Bars represent 100 μm.

FIG. 4. General synthetic scheme of polyol-based polymers. Xylitol (1),sorbitol (2), mannitol (3), and maltitol (4) were polymerized withsebacic acid (5) in different stoichiometries. A simplifiedrepresentation of the polymers is shown. R can be a hydrogen, a polyol,or a sebacic acid molecule.

FIG. 5. (A) Representative ¹H-NMR spectrum of PPS polymers, PMS 1:1 inthis case. Signal intensities of the polyols at 3.5-5.5 ppm, and ofsebacic acid in the polymer were identified at 1.2, 1.5, 2.2 ppm byhydrogens on the carbons labeled ‘a’-‘b’, and ‘c’-‘e’ respectively. (B)FTIR analysis of PPS polymers.

FIG. 6. (A) Typical tensile stress versus strain curves of low Young'smodulus PPS elastomers (PXS 1:1 and PSS 1:1). (B) Typical tensile stressversus strain curves of PPS elastomers with higher Young's moduli. (C)First and last 10 cyclic compression cycles of a 1000 times up to 50 Non PXS 1:1. (D) Block co-polymers composed of low- and high modulus PPSpolymers: PXS 1:1 and PMtS 1:4 respectively, with 25/75, 50/50 and 75/25w/w PXS/PMtS ratios.

FIG. 7. (A) Degradation of PPS polymers in PBS at 37° C. for 105 d. (B)Degradation of PPS polymer in 0.1 N NaOH.

FIG. 8. (A) Attachment and proliferation of HFFs on PPS polymers. The(*) indicates significant difference (p<0.05) to the other PPS polymersfor that time point. Representative phase contrast micrographic imagesof HFFs on PSS 1:1 (B), PSS 1:2 (C), PMS 1:1 (D), PMS 1:2 (E), PMtS 1:4(F), and PLGA (G). Images are 10× magnification. Bars represent 150micron.

FIG. 9. Representative images of H&E stained sections demonstrating theacute inflammatory response to subcutaneous implanted PPS polymers.After 10 days, (A) PSS 1:1, (B) PSS 1:2, (C) PMS 1:1, (D) PMS 1:2, (E)PMtS 1:4 revealed mild inflammatory responses as compared to (F) PLGA.Images are 10× and bars represent 200 μm. P=polymer, C=fibrous capsule,S=skin, and M=muscle.

FIG. 10. Representative images of H&E stained sections demonstrating thechronic inflammatory response to subcutaneous implanted PPS polymers, 12weeks after implantation. The PSS 1:1 elastomer had completely degradedat this time. (A) PSS 1:2, (B) PMS 1:1, (C) PMS 1:2, (D) PMtS 1:4 and(E) PLGA. Images A-D are 20×, and bars represent 100 jam. Image E is10×, and bar represents 200 μm. P=polymer, C=fibrous capsule, S=skin,and M=muscle.

FIG. 11. Initial in vitro analysis of PPS polymers for musculoskeletaltissues. (A) Attachment and subsequent proliferation of an OS cell-linederived from human bone on PMtS 1:4 films, compared to PLGA (i). OS cellmorphology was quantified by cell area (A) (ii) and circularity (C)(iii), also demonstrated by representative phase-contrast images of OScells (iv) and (v) (10×, bars represent 100 μm). (B) Attachment andproliferation of RMS cells derived from human muscle on PSS 1:2 andcompared to PLGA films (i), as well as cell morphology: (ii) for A and(iii) for C (* indicate p<0.05). Representative images (iv) (v)demonstrated the difference (10×, bars represent 100 μm). (C) Seeding ofprimary BACs on PMS 1:2 and PLGA: attachment and subsequent cell numbers(i) (* indicate p<0.05), as well as A (ii) (p<0.05) and C (iv) (p>0.05).Representative images are shown: (iv) and (v). (D) HUVECs attached andproliferated on PXS 1:1 elastomers similar to PLGA (i), and revealedsimilar cell shape (ii) and (iii), also demonstrated by phase contrastimages (iv) and (v) (20×, bars represent 50 μm).

FIG. 12. General synthetic scheme of PXS elastomers. Xylitol waspolymerized with sebacic acid in different stoichiometries. A simplifiedrepresentation of the pre-polymers is shown. R can be a hydrogen, or axylitol or sebacic acid molecule.

FIG. 13. Representative tensile stress versus strain plots of PXSelastomers studied here.

FIG. 14. In vivo behavior of PXS elastomers over time: mass loss (A),sol fraction (B), implant thickness (C), hydration by mass (D),mechanical properties (E) and ΔTg (F).

FIG. 15. Loss of mechanical properties (E0/Et×100%) versus mass loss (%)for PXS elastomers.

FIG. 16. Gross morphology of ex vivo implants: PXS 1:1 implants becameopaque after 1 week (A) but did not swell during degradation, at 2.5(B), and 5 (C) weeks. PXS 1:2 implants remained optically transparentafter 2.5 (D) and 12 (E) weeks, and became slightly opaque after 28 (F)weeks of implantation. PLGA implants (G) became swollen and opaque at 2(H) and 4 (I) weeks.

FIG. 17. SEM micrographs of PXS and PLGA implants. Representative imagesof PXS 1:1 at 1 week (A) (bar represents 50 μm) and at 5 weeks in vivo(B) (bar represents 500 μm), PXS 1:2 at 5 weeks (C) (bar represents 10μm) and at 28 weeks in vivo (D) (bar represents 10 μm), and PLGA at 0weeks (E) (bar represents 30 μm) and at 2 weeks in vivo (F) (barrepresents 100 μm) are shown.

FIG. 18. Representative images of H&E stained sections of subcutaneousimplantation sites of PXS 1:1 elastomers. An overview of the acuteinflammatory response surrounding PXS 1:1 implants at week 1 is shown at2.5× (A) (bar represents 500 μm), and in more detail at 20× (B) (barrepresents 75 μm). An overview of the chronic foreign body responsesurrounding degrading PXS 1:1 implants is shown at 2.5× (C) (barrepresents 500 μm), and in more detail at 20× (D) (bar represents 75μm). The areas of the detailed images are represented in A and C by theblack rectangular. P=polymer, C=fibrous capsule, S=skin and M=muscle.

FIG. 19. Representative images of H&E stained sections of subcutaneousimplantation sites of PXS 1:2 elastomers. An overview of the acuteinflammatory response surrounding PXS 1:2 implants at week 1 is shown at2.5× (A) (bar represents 500 μm), and in more detail at 10× (B) (barrepresents 150 μm). An overview of the chronic foreign body responsesurrounding degrading PXS 1:2 implants at 28 weeks is shown at 5× (C)(bar represents 250 μm), and in more detail at 20× (D) (bar represents75 μm). The areas of the detailed images are represented in A and C bythe black rectangular. P=polymer, C=fibrous capsule, S=skin andM=muscle.

FIG. 20. Representative images of H&E stained sections of subcutaneousimplantation sites of PLGA implants. An overview of the acuteinflammatory response surrounding PLGA implants at week 1 is shown at2.5× (A) (bar represents 500 μm), and in more detail at 10× (B) (barrepresents 150 μm). An overview of the chronic foreign body responsesurrounding degrading PLGA implants at 12 weeks is shown at 5× (C) (barrepresents 250 μm), and in more detail at 20× (D) (bar represents 75μm). The areas of the detailed images are represented in A and C by theblack rectangular. P=polymer, C=fibrous capsule, S=skin and M=muscle.The arrow points to a large vessel of the fibrous capsule surroundingthe PLGA implant.

FIG. 21. Representative images of CD68 stained sections of subcutaneousimplantation sites of PXS and PLGA implants. Recruited and activatedmacrophages are CD68+ (Greaves et al., Int. J. Hemtol. 76(1):6-15,2002). All images are magnified at 20× (bars represent 25 λm). Fibrouscapsules surrounding PXS 1:1 at 1 week (A), 2 weeks (B), and 5 weeks (C)showed CD68+ cells, similar to the PXS 1:2 at 1 week (D), 2 weeks (E)and 12 weeks (F). Fibrous capsules surrounding the PLGA implants seemedto have more CD68+ cells at 1 week (G), 2 weeks (H), and 12 weeks (I).

FIG. 22. Quantitative analysis of in vivo biocompatibility. Fibrouscapsule thicknesses were measured and compared for PXS 1:1, 1:2, andPLGA implants (A) as well as numbers of activated macrophages (CD68+)within the fibrous capsules (B).

FIG. 23. Exemplary acrylated polymers, PXCma and PXSa. The R groups maybe, independently, hydrogen, a suitable hydroxyl protecting group, anacrylate moiety, or other any other group as described herein.

FIG. 24. Exemplary linkage groups formed via polymerization of acrylategroups present on an inventive polymer.

FIG. 25. Reaction of acrylate moieties present on an inventive polymercan also be used to covalently bind biological active structures.

FIGS. 26A-26B. PXC-Aldehyde (PXC-ALD) and PXC-Adipic Dihydrazide(PXC-ADH) In situ Crosslinking. FIG. 26A: Batch 1. Coupling of PXC toadipic dihydrazide; Batch 2: Modification of PXC to provide an aldehydefunctional group; FIG. 26B: Mixing the two batches to provide across-linked polymer.

FIG. 27. Exemplary Reaction Between PXC-ADH and an activated carboxylate(e.g., a modified N-hydroxysuccinimide (NHS)-ester).

FIG. 28. Biologically active agents tethered to amino acids whichcontain nucleophilic oxygen, sulfur, or nitrogen groups.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION

The present invention provides novel polyol-based polymers; novelpolyol-based polymers comprising one or more biologically active agents;pharmaceutical compositions comprising an inventive polyol-basedpolymer; pharmaceutical compositions comprising an inventivepolyol-based polymer and one or more biologically active agents; andmethods of making and using an inventive polyol-based polymer or aninventive polyol-based polymer conjugated to one or more biologicallyactive agents.

Inventive Polymers

In certain aspects of the present invention, a polymer of the presentinvention has the following formula:

wherein:

each instance of Z and L, are, independently, cyclic or acylic, branchedor unbranched, substituted or unsubstituted alkylene; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstitutedalkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkylene; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkenylene; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkynylene;substituted or unsubstituted arylene; substituted or unsubstitutedheteroarylene; or substituted or unsubstituted acylene;

each instance of R^(A) is, independently, hydrogen; Q; —OR^(C); acyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkenyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkynyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkenyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl; or two R^(A) groups are joined to form (═O),(═S), or (═NR^(B)), wherein R^(B) is hydrogen; a suitable aminoprotecting group; substituted or unsubstituted amino; acyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkynyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl;

W is hydrogen, or a suitable carboxylic acid protecting group;

Q is —OR^(C), wherein R^(C) is hydrogen; a suitable hydroxyl protectinggroup; acyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkenyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkynyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkyl; cyclicor acylic, branched or unbranched, substituted or unsubstitutedheteroalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkynyl; substituted or unsubstituted aryl; orsubstituted or unsubstituted heteroaryl; or

Q corresponds to the formula:

wherein:

R^(D) is hydrogen, or a suitable carboxylic acid protecting group;

each instance of j is, independently, 0, 1, or 2;

each instance of k is, independently, 0, 1, or 2;

each instance of m is, independently, 1 to 200;

each instance of n is, independently, 1 to 200; and

each instance of p is, independently, 1 to 1000.

In certain embodiments, R^(A) is hydrogen.

In certain embodiments, j is 0 or 1. In certain embodiments, k is 0 or1.

In certain embodiments, m is 1 to 100. In certain embodiments, m is 1 to50. In certain embodiments, m is 1 to 25. In certain embodiments, m is 1to 10. In certain embodiments, m is 1 to 5. In certain embodiments, m is1 to 4. In certain embodiments, m is 1 to 3. In certain embodiments, mis 1 to 2. In certain embodiments, m is 1.

In certain embodiments, n is 1 to 100. In certain embodiments, n is 1 to50. In certain embodiments, n is 1 to 25. In certain embodiments, n is 1to 10. In certain embodiments, n is 1 to 5. In certain embodiments, n is1 to 4. In certain embodiments, n is 1 to 3. In certain embodiments, nis 1 to 2. In certain embodiments, n is 1.

In certain embodiments, p is 1 to 900. In certain embodiments, p is 1 to800. In certain embodiments, p is 1 to 700. In certain embodiments, p is1 to 600. In certain embodiments, p is 1 to 500. In certain embodiments,p is 1 to 400. In certain embodiments, p is 1 to 300. In certainembodiments, p is 1 to 200. In certain embodiments, p is 1 to 100. Incertain embodiments, p is 1 to 50. In certain embodiments, p is 1 to 25.In certain embodiments, p is 1 to 10. In certain embodiments, p is 1 to5.

In certain embodiments, the term “substituted” includes substitutionwith a “biologically-active agent,” as defined herein. In certainembodiments, the term “substituted” includes substitution with anotherinventive polymer, as defined herein.

In certain embodiments, Z is cyclic or acylic, branched or unbranched,substituted or unsubstituted C₁₋₂₀ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₁₋₂₀ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₁₋₂₀alkynylene, cyclic or acylic, branched or unbranched, substituted orunsubstituted C₁₋₂₀ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₁₋₂₀ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₁₋₂₀heteroalkynylene; or substituted or unsubstituted C₁₋₂₀ acylene.

In certain embodiments, Z is cyclic or acylic, branched or unbranched,substituted or unsubstituted C₁₋₁₅ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₁₋₁₅ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₁₋₁₅alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₁₋₁₅ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₁₋₁₅ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₁₋₁₅heteroalkynylene; or substituted or unsubstituted C₁₋₁₅ acylene.

In certain embodiments, Z is a cyclic or acylic, branched or unbranched,substituted or unsubstituted C₁₋₁₀ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₁₋₁₀ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₁₋₁₀alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₁₋₁₀ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₁₋₁₀ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₁₋₁₀heteroalkynylene; or substituted or unsubstituted C₁₋₁₀ acylene.

In certain embodiments, Z is a cyclic or acylic, branched or unbranched,substituted or unsubstituted C₅₋₁₀ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₅₋₁₀ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₅₋₁₀alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₅₋₁₀ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₅₋₁₀ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₅₋₁₀heteroalkynylene; or substituted or unsubstituted C₅₋₁₀ acylene.

In certain embodiments, Z is acyclic.

In certain embodiments, Z is unbranched.

Additionally, in certain embodiments, Z is unsubstituted. For example,in certain embodiments, each instance of R^(Z) is hydrogen. In certainembodiments, Z corresponds to the formulae:

Alternatively, in certain embodiments, Z is substituted.

In certain embodiments, Z is substituted with one or more oxo; thiooxo;imino; substituted or unsubstituted hydroxyl; substituted orunsubstituted amino; substituted or unsubstituted thiol; acyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkynyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl groups.

In certain embodiments, Z corresponds to the formula:

wherein

each instance of R^(Z) is, independently, hydrogen; acyl; substituted orunsubstituted hydroxyl; substituted or unsubstituted amino; substitutedor unsubstituted thiol; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkenyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkynyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkenyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkynyl; substituted or unsubstitutedaryl; substituted or unsubstituted heteroaryl; nitro; cyano; azido;hydrazino; halo; isocyano; or two R^(Z) groups are joined to form (═O),(═S), or (═NR^(R)), wherein R^(R) is hydrogen; a suitable aminoprotecting group; substituted or unsubstituted amino; acyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkynyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; or substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl; and

each instance of a is, independently, 1 to 20.

In certain embodiments, each instance of a is, independently, 1 to 15.In certain embodiments, each instance of a is, independently, 1 to 10.In certain embodiments, each instance of a is, independently, 1 to 5. Incertain embodiments, each instance of a is 1.

In certain embodiments, Z corresponds to the formula:

wherein

R^(Z) is defined as described herein;

Y is —O—, —S—, or —N(R^(Y))—, wherein R^(Y) is a hydrogen; a suitableamino protecting group; acyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkenyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkynyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkenyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkynyl; substituted or unsubstitutedaryl; or substituted or unsubstituted heteroaryl;

b is, independently, 1 to 20; and

each instance of c is, independently, 0 to 10.

In certain embodiments, b is 1 to 10. In certain embodiments, b is 1 to5. In certain embodiments, b is 1 to 2.

In certain embodiments, c is 1 to 10. In certain embodiments, c is 1 to5. In certain embodiments, c is 1 to 3. In certain embodiments, c is 0.

In certain embodiments, at least one R^(Z) is a —CHO group.

In certain embodiments, at least one R^(Z) is a —CO₂H group.

In certain embodiments, at least one R^(Z) is a —CO₂R^(F1) group,wherein R^(F1) is hydrogen; acyl; a suitable carboxylic acid protectinggroup; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkenyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkynyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkyl; cyclicor acylic, branched or unbranched, substituted or unsubstitutedheteroalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkynyl; substituted or unsubstituted aryl; orsubstituted or unsubstituted heteroaryl.

In certain embodiments, at least one R^(Z) is a —C(O)N(R^(F2))(R^(F3))group, wherein each instance of R^(F2) and R^(F3) is, independently,hydrogen; acyl; substituted or unsubstituted amino; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkenyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkynyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkenyl; cyclic or acylic, branchedor unbranched, substituted or unsubstituted heteroalkynyl; substitutedor unsubstituted aryl; or substituted or unsubstituted heteroaryl.

In certain embodiments, at least one R^(Z) is a substituted orunsubstituted hydroxyl group. In certain embodiments, at least one R^(Z)is a —CHO group and at least one R^(Z) is a hydroxyl group. In certainembodiments, at least one R^(Z) is a —CO₂H group or a —CO₂R^(F1) groupand at least one R^(Z) is a substituted or unsubstituted hydroxyl group.In certain embodiments, at least one R^(Z) is a —C(O)N(R^(F2))(R^(F3))group and at least one R^(Z) is a substituted or unsubstituted hydroxylgroup.

For example, in certain embodiments, Z corresponds to the formulae:

wherein R^(E) is hydrogen or a suitable hydroxyl protecting group;

each instance of d is, independently, 0 to 10, and

R^(Z), and R^(F1) are defined above and herein.

Additionally, in certain embodiments, Z corresponds to the formulae:

wherein d, R^(E), R^(Z), R^(F2) and R^(F3) are defined above and herein.

In certain embodiments, Z corresponds to the formula:

wherein:

each instance of R^(T) is, independently, hydrogen; acyl; substituted orunsubstituted amino; substituted or unsubstituted hydroxyl; substitutedor unsubstituted thiol; acylic, branched or unbranched, substituted orunsubstituted alkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkenyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkynyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkyl; cyclicor acylic, branched or unbranched, substituted or unsubstitutedheteroalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkynyl; substituted or unsubstituted aryl;substituted or unsubstituted heteroaryl, nitro; cyano; azido; hydrazino;halo; isocyano;

each instance of R^(G1) and R^(G2) is, independently, hydrogen; acyl;substituted or unsubstituted amino; a suitable amino protecting group;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkenyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkynyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkenyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl;

each instance of R^(G3) is, independently, hydrogen; acyl; substitutedor unsubstituted amino; a suitable amino protecting group; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkynyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; or substituted or unsubstituted aryl, or two R^(G3)groups are joined to form a doubled bond substituted with acyl; cyclicor acylic, branched or unbranched, substituted or unsubstituted alkyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkynyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl.

g is 1 to 20, and

wherein d, R^(E), R^(F2), R^(Z), are defined above and herein.

In certain embodiments, the group

corresponds to the group:

wherein

e is 1 to 10;

X₁ is —(CR^(X1))₂—, —O—, —S—, or —N(R^(X2))—, wherein R^(X1) is ahydrogen; acyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkenyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkynyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkyl; cyclicor acylic, branched or unbranched, substituted or unsubstitutedheteroalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkynyl; substituted or unsubstituted aryl; orsubstituted or unsubstituted heteroaryl, and R^(X2) is a hydrogen; asuitable amino protecting group; acyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkynyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedheteroalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkenyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkynyl; substituted or unsubstitutedaryl; or substituted or unsubstituted heteroaryl; and

each instance of R^(E) is, independently, a hydrogen; substituted orunsubstituted hydroxyl; substituted or unsubstituted thiol; substitutedor unsubstituted amino; acyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkenyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkynyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkenyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkynyl; substituted or unsubstitutedaryl; substituted or unsubstituted heteroaryl; cyano; isocyano; nitro;halo; hydrazino; or azido.

In certain embodiments, Z corresponds to the formula:

wherein R^(E), R^(F2), and R^(F3) are described above and herein.

In certain embodiments, Z corresponds to the formulae:

wherein R^(E), R^(F2), and R^(F3) are described above and herein.

In certain embodiments, Z corresponds to the formula:

wherein R^(E) and R^(F1) are described above and herein.

In certain embodiments, Z corresponds to the formulae:

wherein R^(E) and R^(F1) are described above and herein.

In certain embodiments, L is cyclic or acylic, branched or unbranched,substituted or unsubstituted C₁₋₂₀ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₁₋₂₀ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₁₋₂₀alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₁₋₂₀ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₁₋₂₀ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₁₋₂₀heteroalkynylene; or substituted or unsubstituted C₁₋₂₀ acylene.

In certain embodiments, L is cyclic or acylic, branched or unbranched,substituted or unsubstituted C₁₋₁₅ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₁₋₁₅ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₁₋₁₅alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₁₋₁₅ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₁₋₁₅ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₁₋₁₅heteroalkynylene; or substituted or unsubstituted C₁₋₁₅ acylene.

In certain embodiments, L is a cyclic or acylic, branched or unbranched,substituted or unsubstituted C₁₋₁₀ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₁₋₁₀ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₁₋₁₀alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₁₋₁₀ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₁₋₁₀ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₁₋₁₀heteroalkynylene; or substituted or unsubstituted C₁₋₁₀-acylene.

In certain embodiments, L is cyclic or acylic, branched or unbranched,substituted or unsubstituted C₅₋₁₀ alkylene; cyclic or acylic, branchedor unbranched, substituted or unsubstituted C₅₋₁₀ alkenylene; cyclic oracylic, branched or unbranched, substituted or unsubstituted C₅₋₁₀alkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted C₅₋₁₀ heteroalkylene; cyclic or acylic, branched orunbranched, substituted or unsubstituted C₅₋₁₀ heteroalkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstituted C₅₋₁₀heteroalkynylene; or substituted or unsubstituted C₅₋₁₀ acylene.

As used herein, when L is “hydroxylated,” at least one carbon atom of Lis substituted with a substituted or unsubstituted hydroxyl group. Asused herein, when L is “partially-hydroxylated,” at least one carbonatom of L is not substituted with a substituted or unsubstitutedhydroxyl group, and at least one carbon atom of L is substituted with asubstituted or unsubstituted hydroxyl group. As used herein, when L is“fully-hydroxylated,” every carbon atom of L is substituted with asubstituted or unsubstituted hydroxyl group. Thus, in certainembodiments, L is hydroxylated; in certain embodiments, L ispartially-hydroxylated; and, in certain embodiments, L isfully-hydroxylated.

For example, in certain embodiments, L is cyclic or acylic, branched orunbranched, hydroxylated C₁₋₂₀ alkylene; cyclic or acylic, branched orunbranched, hydroxylated C₁₋₂₀ alkenylene; cyclic or acylic, branched orunbranched, hydroxylated C₁₋₂₀ alkynylene; cyclic or acylic, branched orunbranched, hydroxylated C₁₋₂₀ heteroalkylene; cyclic or acylic,branched or unbranched, hydroxylated C₁₋₂₀ heteroalkenylene; cyclic oracylic, branched or unbranched, hydroxylated C₁₋₂₀ heteroalkynylene; orhydroxylated C₁₋₂₀ acylene.

In certain embodiments, L is cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₅ alkylene; cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₅ alkenylene; cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₅ alkynylene; cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₅ heteroalkylene; cyclic or acylic, branched orunbranched, hydroxylated C₁₋₁₅ heteroalkenylene; cyclic or acylic,branched or unbranched, hydroxylated C₁₋₁₅ heteroalkynylene; orhydroxylated C₁₋₁₅ acylene.

In certain embodiments, L is a cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₀ alkylene; cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₀ alkenylene; cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₀ alkynylene; cyclic or acylic, branched or unbranched,hydroxylated C₁₋₁₀ heteroalkylene; cyclic or acylic, branched orunbranched, hydroxylated C₁₋₁₀ heteroalkenylene; cyclic or acylic,branched or unbranched, hydroxylated C₁₋₁₀ heteroalkynylene; orhydroxylated C₁₋₁₀ acylene.

In certain embodiments, L is cyclic or acylic, branched or unbranched,hydroxylated C₅₋₁₀ alkylene; cyclic or acylic, branched or unbranched,hydroxylated C₅₋₁₀ alkenylene; cyclic or acylic, branched or unbranched,hydroxylated C₅₋₁₀ alkynylene; cyclic or acylic, branched or unbranched,hydroxylated C₅₋₁₀ heteroalkylene; cyclic or acylic, branched orunbranched, hydroxylated C₅₋₁₀ heteroalkenylene; cyclic or acylic,branched or unbranched, hydroxylated C₅₋₁₀ heteroalkynylene; orhydroxylated C₅₋₁₀ acylene.

In certain embodiments, L is acyclic.

In certain embodiments, L is unbranched.

In certain embodiments, L is hydroxylated, partially hydroxylated, orfully hydroxylated. For example, in certain embodiments, L correspondsto the formulae:

wherein:

each instance of s is, independently, 1 to 6;

each instance of t is, independently, 0 to 5;

each instance of R′ is, independently, hydrogen; a suitable hydroxylprotecting group; acyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkenyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkynyl; cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkenyl; or cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkynyl; substituted orunsubstituted aryl; or substituted or unsubstituted heteroaryl; or R′corresponds to the formulae:

wherein:

each instance of u is, independently, 0 to 5;

each instance of v is, independently, 1 to 6;

each instance of R″ is, independently, hydrogen; acyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkenyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkynyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkenyl; cyclic or acylic, branchedor unbranched, substituted or unsubstituted heteroalkynyl; orsubstituted or unsubstituted aryl;

each instance of R′″ is, independently, hydrogen; halo; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkynyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkenyl; or cyclic oracylic, branched or unbranched, substituted or unsubstitutedheteroalkynyl; substituted or unsubstituted aryl; or substituted orunsubstituted heteroaryl;

each instance of R″″ is —(OR^(X)), wherein R^(X) is hydrogen; a suitablecarboxylic acid protecting group; acyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkenyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkynyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedheteroalkyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkenyl; or cyclic or acylic, branched orunbranched, substituted or unsubstituted heteroalkynyl; substituted orunsubstituted aryl; or substituted or unsubstituted heteroaryl; or R″″corresponds to the formula:

and wherein L, Q, W, R′, R″, R^(A), R^(Z), R^(T), R^(G1), R^(G2),R^(G3), g, s, t, m, n, j, k, p, and g, are defined above and herein.

In certain embodiments, the ratio of m to n is about 1:1; 2:1; 3:1;4:5:1; 6:1; 7:1; 8:1; 9:1; or 10:1. In certain embodiments, the ratio ofm to n is 1:2; 1:3; 1:4; 1:5; 1:6; 1:7; 1:8; 1:9; or 1:10. In certainembodiments, the ratio of m to n is 2:3, 3:2, 3:4, or 4:3. In certainembodiments, the polymer is the result of a mixture of two or moredifferent ratios. The ratio of m to n, inherently, represents the ratioof polyol to polycarboxylic acid used to form the inventive polymer.

In certain embodiments, R′ is hydrogen. In certain embodiments, R″ ishydrogen.

In certain embodiments, t is 0. In certain embodiments, each instance ofs is, independently, 2 to 6. In certain embodiments, each instance of sis, independently, 2 to 5. In certain embodiments, each instance of sis, independently, 2 to 4. In certain embodiments, s is 3 to 5. Incertain embodiments, s is 3.

In certain embodiments, L corresponds to the formulae:

or L is a mixture thereof.

In certain embodiments, L corresponds to the formulae:

L is a mixture thereof,wherein R′ is defined above and herein.

In certain embodiments, L corresponds to the formulae:

or L is a mixture thereof, wherein R′ is defined above and herein.

In certain embodiments, L corresponds to the formulae:

or L is a mixture thereof, wherein R′ is defined above and herein.

In certain embodiments, L corresponds to the formula:

wherein R′ is defined above and herein.

In certain embodiments, L corresponds to a polyol selected from Table 1(provided below). In certain embodiments, L corresponds to a polyolselected from glycerol, erythritol, threitol, ribitol, arabinitol,xylitol, allitol, altritol, galactritol, sorbitol, mannitol, iditol,lactitol, isomalt, or maltitol, wherein the functional groups present onthe polyol are optionally substituted, as described above. In certainembodiments, L corresponds to a polyol selected from xylitol, mannitol,sorbitol, or maltitol, wherein the functional groups present on thepolyol are optionally substituted, as described above.

TABLE 1 Exemplary polyols Sugar alcohols

Cyclic sugars Maltitol, lactitol, isomalt

e.g., monosaccharides which include hexoses (allose, altrose, glucose,mannose, gulose, idose, galactose, talose) and pentoses (ribose,arabinaose, xylose, lyxose); disaccharides which include maltose,cellobiose. sucrose, and lactose; polysaccharides which include amylose,amylopectin, glycogen, and cellulose; fructofuranose, glucopyranose.sorbose, rhaminose, tagatose, apiose, deoxyribose, ribofructose,1,3.6-tri-O-galloyl-β-D- glucopyranose (tannic acid); amino- containingcyclic sugars (e.g., N-acetyl glucoseamine (sialic acid), glucoseamine);amide-containing cyclic sugars (e.g., glucoronamide); carboxylcontaining sugars (e.g., galacturonic acid); as well as protectedderivatives, such as alkyl- and acyl- derivatives, and stereoisomersthereof. Pentaerythritols, and structural derivatives thereof, such asmethylated, ethylated, acetate, ethoxylale, and propoxylate derivatives.

Phenolic polyols e.g., resorcinol, orcinol, 2-methylresorcinol,phloroglucinol, 1,2,4 benzenetriol, pyrogallol, 4- ethylresorcinol.5-methyl benzene 1,2,3triol, 2- methoxyhydroquinone, 3,5dihydroxylbenzylalcohol, 2,4,6 trihydroxytoluene, 2,4,5- trihydroxybenzaldehyde, 2,3,4-trihydroxybenzaldehyde, 2,4,6,- trihydroxybenzaldehyde,gallacetophenone, 3,4,5-trihydroxybenzamide, gallic acid, 2,4,5-trihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid,2-nitrophloroglucinol; naturally occurring phenolic compounds, such ascarnosol, rosmanol (7α-), epirosmanol (7β-) from rosemary (Rosmarinusofficialis L.); rosemaric acid from rosemary and oregano (Oreganumvulgare L.); capsicin and dihydrocapsicin, hot-lasting compounds, fromhot pepper (Capsicinum annuum L.); ferulic acid amide of tyramine fromblack pepper (Piper nigrum L.); piperin-relatcd compound from thyme(Thymus serpyllum L.); and apigenin and apiin from parsley Miscellaneouspolyols

In certain embodiments, Z corresponds to a polycarboxylic acid selectedfrom Table 2 (provided below). In certain embodiments, Z corresponds toa polycarboxylic acid selected from the group consisting of succinicacid, fumaric acid, α-ketoglutaric acid, oxaloacetic acid, malic acid,oxalosuccinic acid, isocitric acid, cis-aconitic acid, citric acid,2-hydroxy-malonic acid, tartaric acid, ribaric acid, arabinaric acid,xylaric acid, allaric acid, altraric acid, galactaric acid, glucaricacid, or mannaric acid, dimercaptosuccinic acid, oxalic acid, malonicacid, succinic acid, glutaric acid, adipic acid, pimelic acid, subericacid, azelaic acid, and sebacic acid, wherein the functional groupspresent on polycarboxylic acids are optionally substituted, as describedabove. In certain embodiments, Z corresponds to citric acid. In certainembodiments, Z corresponds to sebacic acid. In certain embodiments Zcorresponds to a polycarboxylic acid selected from glutaric acid, citricacid and sebacic acid, wherein the functional groups present onpolycarboxylic acids are optionally substituted, as described herein.

TABLE 2 Exemplary Polycarboxylic Acids Oxalic acid

Malonic acid (propanedioic acid)

Succinic acid, succinate (butanedioic acid)

Glutaric acid (pentanedioic acid)

Adipic acid (hexanedioic acid)

Pimelic acid (heptanedioic acid)

Suberic acid (octanedioic acid)

Azelaic acid (nonanedioic acid)

Sebaic acid (decanedioic acid)

Aldaric acids

Aspartic acid

DMSA (Dimercapto-succinic acid, 2,3- bis-sulfanylbutanedioic acid)

fumaric acid

maleic acid

glutaconic acid

glutamic Acid, Gln, Glutamate

α-ketoglutaric acid; Oxopentanedioic acid;

β-ketoglutaric acid

Oxaloacetic acid; Oxaloacetate;

Malic acid; Malate; hydroxysuccininc acid

fumaric acid; fumarate

oxalosuccininc acid: oxalosuccinate

isocitric acid: isocitrate

cis-aconitic acid

Citric acid; citrate

Itaconic acid: methylenesuccininc acid

mesaconic acid: (2E)-2- Methyl-2-butenedioic acid

Tartaric acid, 2-3- dihydroxybutanedioic acid,, 3- dihydroxysuccinicacid; thearic acid; uvic acid; paratartaric acid

Traumatic acid; dodec-2- enedioic acid

In certain embodiments, the polymer is of the formula:

wherein:

each instance of Z, is, independently, cyclic or acylic, branched orunbranched, substituted or unsubstituted alkylene; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstitutedalkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkylene; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkenylene; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkynylene;substituted or unsubstituted arylene; substituted or unsubstitutedheteroarylene; or substituted or unsubstituted acylene;

W is hydrogen, or a suitable carboxylic acid protecting group;

Q is —OR^(C), wherein R^(C) is hydrogen; a suitable hydroxyl protectinggroup; acyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted alkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted alkenyl; cyclic or acylic, branched orunbranched, substituted or unsubstituted alkynyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkyl; cyclicor acylic, branched or unbranched, substituted or unsubstitutedheteroalkenyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkynyl; substituted or unsubstituted aryl; orsubstituted or unsubstituted heteroaryl;

or Q corresponds to the formula:

wherein:

R^(D) is hydrogen or a suitable carboxylic acid protecting group;

each instance of s is, independently, 1 to 6;

each instance of m is, independently, 1 to 200;

each instance of n is, independently, 1 to 200; and

each instance of p is, independently, 1 to 1000.

In certain embodiments, the polymer is of the formula:

In certain embodiments, the polymer is of the formula:

wherein each occurrence of w is 1 to 20, inclusive. In certainembodiments, w is 4. In certain embodiments, w is 6. In certainembodiments, w is 8. In certain embodiments, w is 10. In certainembodiments, w is 12. In certain embodiments, w is 14.

In certain embodiments, the polymer is based on the polyol xylitol is ofthe formula:

wherein

each occurrence of f is an integer between 0 and 1, inclusive;

p is an integer between 1 and 1000, inclusive;

each occurrence of Q is, independently, —OR^(C), wherein R^(C) ishydrogen; a suitable hydroxyl protecting group; acyl; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkyl; cyclic oracylic, branched or unbranched, substituted or unsubstituted alkenyl;cyclic or acylic, branched or unbranched, substituted or unsubstitutedalkynyl; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkyl; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkenyl; cyclic or acylic, branchedor unbranched, substituted or unsubstituted heteroalkynyl; substitutedor unsubstituted aryl; or substituted or unsubstituted heteroaryl; or

Q corresponds to the formula:

wherein R^(D) is hydrogen or a suitable carboxylic acid protectinggroup;

each occurrence of Z is, independently, cyclic or acylic, branched orunbranched, substituted or unsubstituted alkylene; cyclic or acylic,branched or unbranched, substituted or unsubstituted alkenylene; cyclicor acylic, branched or unbranched, substituted or unsubstitutedalkynylene; cyclic or acylic, branched or unbranched, substituted orunsubstituted heteroalkylene; cyclic or acylic, branched or unbranched,substituted or unsubstituted heteroalkenylene; cyclic or acylic,branched or unbranched, substituted or unsubstituted heteroalkynylene;substituted or unsubstituted arylene; substituted or unsubstitutedheteroarylene; or substituted or unsubstituted acylene; and

each occurrence of W is, independently, hydrogen or a suitablecarboxylic acid protecting group. As would be appreciated by one ofskill in the art, analogous polymers may be prepared using other polyolssuch as sorbitol or mannitol.

In another aspect, the present invention provides a branched polymercomprising alternating polyol and polycarboxylic acid units, wherein thepolycarboxylic acid(s) used to form the polymer comprises at least two(2) carboxylic acid groups, and the polyol(s) used to form the polymercomprises at least three (3) hydroxyl groups. In certain embodiments,the branched polymer comprises one or more polyols. In certainembodiments, the branched polymer comprises one or more polycarboxylicacids.

In certain embodiments, the polyol(s) used to form the polymer has atleast two (2) hydroxyl groups. In certain embodiments, the polyol(s)used to form the polymer has at least three (3) hydroxyl groups. Incertain embodiments, the polyol(s) used to form the polymer has at leastfour (4) hydroxyl groups. In certain embodiments, the polyol(s) used toform the polymer has at least five (5) hydroxyl groups. In certainembodiments, the polyol(s) used to form the polymer has at least six (6)hydroxyl groups. In certain embodiments, the polyol(s) used to form thepolymer has at least seven (7) hydroxyl groups. In certain embodiments,the polyol(s) used to form the polymer has at least eight (8) hydroxylgroups. In certain embodiments, the polyol(s) used to form the polymerincludes between 3 to 10 hydroxyl groups. In certain embodiments, thepolyol(s) used to form the polymer includes between 3 to 6 hydroxylgroups. Exemplary polyols used to form the inventive polymer include,but are not limited to, those depicted and listed in Table 1.

The polycarboxylic acid(s) used to form the polymer may further includeat least two (2), three (3), four (4), five (5), or six (6) carboxylicacid groups. In certain embodiments, the polycarboxylic acid(s) used toform the polymer includes between two (2) to six (6) carboxylic acidgroups. In certain embodiments, the polycarboxylic acid(s) used to formthe polymer is a dicarboxylic acid (e.g., contains two carboxylic acidgroups). In certain embodiments, the polycarboxylic acid(s) used to formthe polymer is a tricarboxylic acid (e.g., contains three carboxylicacid groups). In certain embodiments, the polycarboxylic acid(s) issymmetrical. Exemplary polycarboxylic acids used to form the inventivepolymer include, but are not limited to, those depicted and listed inTable 2.

In certain embodiments, the ratio of polyol to polycarboxylic acid(which also correspond to the variables m and n, respectively, in theformulae provided herein) in the polymer is about 1 to 1; 1 to 1.25; 1to 1.5; 1 to 1.75; 1 to 2; 1 to 2.25; 1 to 2.50; 1 to 2.75; 1 to 3; 1 to3.25; 1 to 3.50; 1 to 3.75; 1 to 4; 1 to 4.25; 1 to 4.50; 1 to 4.75; 1to 5; 1 to 5.25; 1 to 5.50; 1 to 5.75; 1 to 6; 1 to 6.25; 1 to 6.50; 1to 6.75; 1 to 7; 1 to 7.25; 1 to 7.50; 1 to 7.75; 1 to 8; 1 to 8.25; 1to 8.50; 1 to 8.75; 1 to 9; 1 to 9.25; 1 to 9.50; 1 to 9.75; or 1 to 10molecules of polyol to molecules of polycarboxylic acid.

In certain embodiments, the ratio of polyol to polycarboxylic acid inthe polymer is 1 to 1.

In certain embodiments, the ratio of polyol to polycarboxylic acid inthe polymer is 1 to 2.

In certain embodiments, the ratio of polyol to polycarboxylic acid(which also correspond to the variables m and n, respectively, in theformulae provided herein) in the polymer is about 2 to 1; 2.25 to 1;2.50 to 1; 2.75 to 1; 3 to 1; 3.25 to 1; 3.50 to 1; 3.75 to 1; 4 to 1;4.25 to 1; 4.50 to 1; 4.75 to 1; 5 to 1; 5.25 to 1; 5.50 to 1; 5.75 to1; 6 to 1; 6.25 to 1; 6.50 to 1; 6.75 to 1; 7 to 1; 7.25 to 1; 7.50 to1; 7.75 to 1; 8 to 1; 8.25 to 1; 8.50 to 1; 8.75 to 1; 9 to 1; 9.25 to1; 9.50 to 1; 9.75 to 1; or 10 to 1 molecules of polyol to molecules ofpolycarboxylic acid.

In certain embodiments, wherein the inventive polymer comprises twodifferent polyols, the two polyols may be present in a ratio of about 1to 1; 1 to 1.25; 1 to 1.5; 1 to 1.75; 1 to 2; 1 to 2.25; 1 to 2.50; 1 to2.75; 1 to 3; 1 to 3.25; 1 to 3.50; 1 to 3.75; 1 to 4; 1 to 4.25; 1 to4.50; 1 to 4.75; 1 to 5; 1 to 5.25; 1 to 5.50; 1 to 5.75; 1 to 6; 1 to6.25; 1 to 6.50; 1 to 6.75; 1 to 7; 1 to 7.25; 1 to 7.50; 1 to 7.75; 1to 8; 1 to 8.25; 1 to 8.50; 1 to 8.75; 1 to 9; 1 to 9.25; 1 to 9.50; 1to 9.75; or 1 to 10. In certain embodiments, the inventive polymer is amixture of two or more ratios of polyols.

In certain embodiments, wherein the inventive polymer comprises twodifferent polycarboxylic acids, the two polycarboxylic acids may bepresent in a ratio of about 1 to 1; 1 to 1.25; 1 to 1.5; 1 to 1.75; 1 to2; 1 to 2.25; 1 to 2.50; 1 to 2.75; 1 to 3; 1 to 3.25; 1 to 3.50; 1 to3.75; 1 to 4; 1 to 4.25; 1 to 4.50; 1 to 4.75; 1 to 5; 1 to 5.25; 1 to5.50; 1 to 5.75; 1 to 6; 1 to 6.25; 1 to 6.50; 1 to 6.75; 1 to 7; 1 to7.25; 1 to 7.50; 1 to 7.75; 1 to 8; 1 to 8.25; 1 to 8.50; 1 to 8.75; 1to 9; 1 to 9.25; 1 to 9.50; 1 to 9.75; or 1 to 10. In certainembodiments, the inventive polymer is a mixture of two or more ratios ofpolycarboxylic acids.

The hydroxyl substituents present on the polyol used to form thepolymer, and those which may, optionally, be present on thepolycarboxylic acid unit, are either free hydroxyl groups (i.e., —OH) orare optionally substituted with an acyl group (such as an acrylategroup, or an ester group formed from condensation with a polycarboxylicacid molecule), aliphatic, or a suitable hydroxyl protecting group.Additionally, two hydroxyl groups may be covalently conjugated to eachother via a bridging acyl linkage, alkylene, or heteroalkylene linkage,and the two hydroxyl groups may be present on the same polymeric chain,or on different polymeric chains. In the case of the formation of acovalent bond or bridge between two different polymeric chains, thebranched polymer may also be referred to as a “cross-linked polymer.” Incertain embodiments, the hydroxyl groups of the polyol and thepolycarboxylic acid used to form the inventive polymer are free hydroxylgroups.

Additionally, one or more carboxylic acid substituents which may bepresent on a polycarboxylic acid unit may, optionally, be covalentlyconjugated via a bridging acyl linkage, alkylene, or heteroalkylenelinkage, and the two carboxylic acid groups so joined may be present onthe same polymeric chain, or on different polymeric chains. In the caseof the formation of a covalent bond or bridge between two differentpolymeric chains, the branched polymer may also be referred to as a“cross-linked polymer.” In certain embodiments, the hydroxyl groups ofthe polyol and the polycarboxylic acid used to form the inventivepolymer are free hydroxyl groups.

The polyol and polycarboxylic acid used to form the polymer of thepresent invention, the polyol and/or the polycarboxylic acid may bepresent in its salt-free form, or may be a salt-form thereof. Exemplarypharmaceutically salts are described herein. Each of the polyols andpolycarboxylic acids, as well, may be derivatives of known polyols andpolycarboxylic acids; for example, a synthetic derivative (a carboxylicacid, an ester, an amide, and an acyl chloride are syntheticderivatives), or a synthetic analog. Derivatives and analogs may besynthesized from the inventive compound or polymer itself, or from otherstarting materials to make structural versions of the compound orpolymer.

In certain aspects of the present invention, the polyol monomer used inthe formation of the inventive polymer is an organic compound found innature, or derived from nature. Such a compound can either besynthesized in a laboratory or isolated from natural sources. In certainembodiments, the polyol is endogenous to the human metabolic system. Incertain embodiments, the polyol is non-toxic. In certain embodiments,the polyol is an optically enriched polyol. In certain embodiments, thepolyol is an aliphatic polyol (i.e., does not contain arylene orheteroarylene groups).

In certain embodiments, the polyol is a food additive. Exemplary foodadditives include lactitol, isomalt, maltitol, and sugar alcohols.Exemplary sugar alcohols include glyceritol (i.e., glycerol),erythritol, threitol, ribitol, arabinitol, xylitol, allitol, altritol,galactritol, sorbitol, mannitol, and iditol.

In certain embodiments, the polyol is erythritol, threitol, ribitol,arabinitol, xylitol, allitol, altritol, galactritol, sorbitol, mannitol,iditol, lactitol, isomalt, or maltitol. In certain functions. Exemplaryaldaric acids include 2-hydroxy-malonic acid, tartaric acid, ribaricacid, arabinaric acid, xylaric acid, allaric acid, altraric acid,galactaric acid, glucaric acid, or mannaric acid.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer comprises an optionally substituted alkanedioicacid. The term “alkanedioic acid,” as used herein, refers to adicarboxylic acid having the formula HO(O═)C—(CH₂)_(x)—C(═O)OH, whereinx is an integer of between 1 to 20, inclusive. When x is 1, thealkanedioic acid may be referred to as a “C₁ alkanedioic acid.” When xis 20, the alkanedioic acid may be referred to as a “C₂₀ alkanedioicacid.” In certain embodiments, the alkanedioic acid is a C₁-C₂₀alkanedioic acid, a C₁-C₁₅ alkanedioic acid, a C₁-C₁₀ alkanedioic acid,a C₁-C₁₂ alkanedioic acid, a C₁-C₁₀ alkanedioic acid, a C₅-C₁₅alkanedioic acid, a C₅-C₁₂ alkanedioic acid, a C₅-C₁₀ alkanedioic acid,or a C₈-C₁₂ alkanedioic acid. Exemplary alkanedioic acids includedimercaptosuccinic acid, oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, orsebacic acid.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer comprises an optionally substituted alkenedioicacid. The term “alkenedioic acid,” as used herein, refers to analkanedioic acid, as defined herein, with at least one internal doublebond, e.g., HO(O═)C—(CH═CH)_(z)—(CH₂)_(y)—C(═O)OH), wherein (2z+y) is aninteger between 2 to 20. For example, when y is 0 and z is 1, thealkenedioic acid may be referred to as a “C₂ alkenedioic acid.” When(2z+y) equals 20, the alkenedioic acid may be referred to as a “C₂₀alkenedioic acid.” Exemplary alkenedioic acids include fumaric acid,maleic acid, glutaconic acid, itaconic acid, mesaconic acid, ortraumatic acid.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer is an optionally substituted glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, or sebacic acid. Incertain embodiments, the polycarboxylic acid is optionally substitutedglutaric acid. In certain embodiments, the polycarboxylic acid isoptionally substituted sebacic acid. In certain embodiments, the polymerformed from an alkanedioic acid and the polyol glycerol is specificallyexcluded. In certain embodiments, the polymer formed from sebacic acidand the polyol glycerol is specifically excluded. In certainembodiments, the polymer formed from citric acid and the polyol glycerolis specifically excluded. Furthermore, in certain embodiments, thepolymer formed from glutaric acid and the polyol glycerol isspecifically excluded.

In certain embodiments, the inventive polymer comprises a polyol fromTable 1, and a polycarboxylic acid from Table 2. In certain embodiments,the polyol is a sugar alcohol and the polycarboxylic acid is ametabolite, as described above and herein. In certain embodiments, thepolyol is a sugar alcohol and the polycarboxylic acid is an optionallysubstituted alkanedioic acid, as described above and herein.

In certain embodiments, the polyol is xylitol, mannitol, sorbitol, ormaltitol and the polycarboxylic acid is a metabolite. In certainembodiments, the polyol is xylitol, mannitol, sorbitol, or maltitol, andthe polycarboxylic acid is citric acid.

In certain embodiments, the polyol is xylitol, mannitol, sorbitol, ormaltitol and the polycarboxylic acid is an optionally substitutedalkanedioic acid. In certain embodiments, the polyol is xylitol,mannitol, sorbitol, or maltitol and the polycarboxylic acid isoptionally substituted glutaric acid. In certain embodiments, the polyolis xylitol, mannitol, sorbitol, or maltitol and the polycarboxylic acidis optionally substituted sebacic acid.

Properties of the Inventive Polymers

In certain aspects, the inventive polymer is biodegradable. In certainaspects, the inventive polymer is non-toxic. In certain embodiments, theinventive polymer, upon biodegrading, degrades to non-toxic products. Incertain embodiments, the non-toxic products are endogenous to the humanmetabolic system. In certain embodiments, the non-toxic products are notharmful to the environment. In certain embodiments, the non-toxicproducts are not harmful to humans. In certain embodiments, thenon-toxic products have been (or will be) approved by the U.S. Food andDrug Administration as safe for human consumption or medicalapplications.

Thus, in one aspect of the present invention, the inventive polymer,upon biodegrading, degrades to non-toxic alcohols. In certainembodiments, the non-toxic alcohols are sugar alcohols. In certainembodiments, the non-toxic alcohols are biologically active. In certainaspects, the activity of the biologically active alcohols compriseantimicrobial, antifungal, and/or antibacterial activity. In certainaspects, the biologically active alcohol is xylitol. The safety andadministration of xylitol as a nutrient and medicament to humans hasbeen well-documented (see, for example, Uhari et al., Vaccine (2001)19:S144-S147; Pizzo et al., Microbiologica (2000) 23:63-71; Brown etal., Laryngoscope (2004) 114:2021-2024; Mattila et al., Metabolism(2002) 51:92-96; Mattila et al., Journal of Nutrition, (1998) 1811-1814;and Ly et al., Pediatric Dentistry (2006) 28:154-163).

In certain aspects, the inventive polymer is a substantially clearpolymer. “Substantially clear” refers to a sample specimen with a lighttransmission percentage of at least 85%, or greater, and, optionally,when the refractive index is constant through the sample in the viewingdirection. In certain embodiments, the light transmission percentage isat least about 85%, 90%, 95%, or 99%.

In certain aspects, the inventive polymer is pH responsive. As usedherein “pH responsive” refers to a change in the physical properties(e.g., swelling-deswelling as the pH drops/rises; morphology;solubility; elasticity) of an inventive polymer as a result of a changein the pH of its environment. For example, an inventive polymer which issolubilized, partially-solubilized, or suspended in a suitable mediummay be exposed to a change in the pH of the medium (the pH may beacidic, basic, or neutral). In certain embodiments, the suitable mediumcomprises water, a polar protic solvent such as water or alcohol (e.g.,methanol, ethanol, isopropanol), a polar aprotic solvent (e.g.,dimethylformamide (DMF), dimethylacetamide (DMA), dimethylsulfoxide(DMSO), N-methylpyrrolidinone (NMP)), ethers (e.g., diethyl ether,dioxane, tetrahydrofuran (THF)), halogenated hydrocarbons (e.g.,dichloromethane (DCM), dichloroethane (DCE), chloroform), aromaticsolvents (e.g., toluene, benzene), or a mixture thereof.

A polymer of the presently claimed invention may take on many differentforms, properties, 3-dimensional shapes, and/or sizes. For example, incertain embodiments, the inventive polymer is a bead, microsphere,nanoparticle, pellet, matrix, mesh, gauze, strand, thread, fiber, film,or coating. In certain embodiments, the inventive polymer has adisc-like or spheroidal-like shape.

In certain embodiments, the inventive polymer is a plastic (e.g., ismalleable, having the property of plasticity). In certain embodiments,the inventive polymer is a thermoplastic. In certain embodiments, thepolymer is a thermoset polymer.

In certain embodiments, the inventive polymer is a paste or a wax or hasa paste-like or wax-like consistency.

In certain embodiments, the inventive polymer is water soluble, orpartially water soluble. In certain embodiments, the inventive polymeris not water soluble.

In certain embodiments, the inventive polymer is a hydrogel.

In certain embodiments, the inventive polymer is a stiff, hardbiomaterial (e.g., is not malleable). In certain embodiments, theinventive polymer is a brittle biomaterial.

As used herein, a hydrogel is a polymer which absorbs at least about 10wt % of water (in the presence of an abundance of water). In certainembodiments, the hydrogel polymer absorbs between about 10 to 100%, 10to 90 wt %, 10 to 80 wt %, 10 to 70 wt %, 10 to 60 wt %, 10 to 50 wt %,10 to 40 wt %, 10 to 30 wt %, 10 to 20 wt %, or 10 to 15 wt % of water.In certain embodiments, the hydrogel polymer has an in-vivo half life ofbetween about 1 week to 2 years. In certain embodiments, the hydrogelhas an in-vivo half life of at least about 1 week, 2 weeks, 3 weeks, 4weeks, 2 months, 3 months, 4 months, 5 months, 6 months, 7 months, 8months, 9 months, 10 months, 11 months, 1 year, 1.5 years, or 2 years.In certain embodiments, the ratio of polyol to polycarboxylic acid inthe hydrogel is 1 to 1.

In certain embodiments, the inventive polymer is an elastomer.Elastomers include tough elastomers and hydrated elastomers.

In certain embodiments, the inventive polymer is a tough elastomer(i.e., an elastomer which is not a hydrogel). In certain embodiments,the tough elastomer absorbs between about 0 to 9.5% water. In certainembodiments, the tough elastomer has an in-vivo half life of betweenabout 1 week to 2 years. In certain embodiments, the tough elastomer hasan in-vivo half life of at least about 1 week, 2 weeks, 3 weeks, 4weeks, 2 months, 3 months, 4 months, months, 6 months, 7 months, 8months, 9 months, 10 months, 11 months, 1 year, 1.5 years, or 2 years.In certain embodiments, the tough elastomer does not sustain permanentstructural deformation upon stretching the polymer between about 1 to 2,1 to 6, 1 to 8, 1 to 10, 1 to 20, 1 to 30, 1 to 40, 1 to 50, 1 to 60, 1to 70, 1 to 80, 1 to 90, 1 to 100, 1 to 150, 1 to 200, 1 to 250, or 1 to300% of its original length. In certain embodiments, the tough elastomerhas a Young's moduli of at least about 0.5 to about 12 MPa. In certainembodiments, the tough elastomer has a Young's moduli of at least about0.5 to about 6 MPa. In certain embodiments, the hydrated elastomer has aYoung's moduli of about 12 MPa.

In certain embodiments, the tough elastomer maintains athree-dimensional shape. In certain embodiments, the ratio of polyol topolycarboxylic acid in the tough elastomer is 1 to 2.

In certain embodiments, the polymer is a hydrated elastomer (i.e.,having the properties of both a hydrogel and an elastomer). In certainembodiments, the hydrated elastomer has an in-vivo half life of betweenabout 1 week to about 2 years. In certain embodiments, the hydratedelastomer has an in-vivo half life of at least about 1 week, 2 weeks, 3weeks, 4 weeks, 2 months, 3 months, 4 months, 5 months, 6 months, 7months, 8 months, 9 months, 10 months, 11 months, 1 year, 1.5 years, or2 years. In certain embodiments, the hydrated elastomer absorbs betweenabout 10 to 100%, 10 to 90 wt %, 10 to 80 wt %, 10 to 70 wt %, 10 to 60wt %, 10 to 50 wt %, 10 to 40 wt %, 10 to 30 wt %, 10 to 20 wt %, or 10to 15 wt % of water. In certain embodiments, the hydrated elastomer doesnot sustain permanent structural deformation upon stretching the polymerbetween about 1 to 2, 1 to 6, 1 to 8, 1 to 10, 1 to 20, 1 to 30, 1 to40, 1 to 50, 1 to 60, 1 to 70, 1 to 80, 1 to 90, 1 to 100, 1 to 150, 1to 200, 1 to 250, or 1 to 300% of its original length. In certainembodiments, the hydrated elastomer has a Young's moduli of at leastabout 0.5 to about 12 MPa. In certain embodiments, the hydratedelastomer has a Young's moduli of at least about 0.5 to about 6 MPa. Incertain embodiments, the hydrated elastomer has a Young's moduli ofabout 12 MPa.

In certain embodiments, an inventive elastomeric polymer is obtained byreacting a water soluble polyol with a water insoluble polycarboxylicacid. In certain embodiments, an inventive elastomeric polymer isobtained by reacting a water insoluble polyol with a water solublepolycarboxylic acid. In certain embodiments, an inventive elastomericpolymer is obtained by reacting a water insoluble polyol with a waterinsoluble polycarboxylic acid.

In certain embodiments, an inventive hydrogel polymer is obtained byreacting a water soluble polyol with a water soluble polycarboxylicacid.

In certain embodiments, an inventive hydrogel polymer is obtained byfirst reacting a water soluble polyol with a water solublepolycarboxylic acid, and then cross-linking the polymer in an aqueousenvironment.

In another aspect of the present invention, the inventive polymerfurther comprises, or is further modified with, a biologically activeagent. In certain embodiments, the inventive polymer comprises at leastone biologically active agent. In certain embodiments, the inventivepolymer comprises at least two biologically active agents.

As used herein, a “biologically active agent” or “active agent,” refersto therapeutic cells, organic molecules (e.g., drug compounds), peptides(e.g., dipeptides, polypeptides, proteins), antibodies, modifiedantibodies, receptors, aptamers, drug/peptide modified amino acids,enzymes, carbohydrates (e.g., monosaccharides, oligosaccharides,polysaccharides), nucleoproteins, mucoproteins, lipoproteins,glycoproteins, steroids, nucleic acids, DNAs, RNAs, nucleotides,nucleosides, polynucleotides, antisense oligonucleotides, lipids,hormones, and vitamins, metals, transition metals, or a combinationthereof.

In certain embodiments, the biologically active agent is covalentlyconjugated to the polymer. In certain embodiments, the biologicallyactive agent is covalently conjugated to the inventive polymer via anester or amide linkage.

In certain embodiments, the biologically active agent is non-covalentlyconjugated to the polymer. In certain embodiments, the biologicallyactive agent is entrapped (e.g., encapsulated) by the inventive polymer.

In certain embodiments, the biologically active agent is a “prodrug”when conjugated to the inventive polymer, and is administered to asubject in an inactive (or significantly less active) form. Onceadministered, the conjugated prodrug is metabolised in vivo, forexample, by deacylation, dephosphorylation, hydrolysis, orepimerization, to a more active form.

However, in certain embodiments, the biologically active agent is asactive, or partially active, when conjugated to the polymer (or whenentrapped by the polymer) as compared to the free biologically activeagent (i.e., not conjugated or entrapped).

In certain embodiments, the biologically active agent is a cell.Exemplary cells include immune system cells (e.g., mast cell,lymphocyte, plasma cell, macrophage, dendritic cell, neutrophils,eosinophils), connective tissue cells (e.g., blood cells, erythrocytes,leucocytes, megakaryocytes, fibroblasts, osteoclasts), stem cells (e.g.,embryonic stem cells, adult stem cells), bone cells, glial cells,pancreatic cells, kidney cells, nerve cells, skin cells, liver cells,muscle cells, adipocytes, Schwann cells, Langerhans cells, as well as(micro)-tissues such as the Islets of Langerhans.

In certain embodiments, the biologically active agent is a small organicmolecule. In certain embodiments, a small organic molecule isnon-peptidic. In certain embodiments, a small organic molecule isnon-oligomeric. In certain embodiments, a small organic molecule is anatural product or a natural product-like compound having a partialstructure (e.g., a substructure) based on the full structure of anatural product. Exemplary natural products include steroids,penicillins, prostaglandins, venoms, toxins, morphine, paclitaxel(Taxol), morphine, cocaine, digitalis, quinine, tubocurarine, nicotine,muscarine, artemisinin, cephalosporins, tetracyclines, aminoglycosides,rifamycins, chloramphenicol, asperlicin, lovastatin, cyclosporin,curacin A, eleutherobin, discodermolide, bryostatins, dolostatins,cephalostatins, antibiotic peptides, epibatidine, α-bungarotoxin,tetrodotoxin, teprotide, and neurotoxins from Clostridium botulinum. Incertain embodiments, a small organic molecule is a drug approved by theFood and Drugs Administration as provided in the Code of FederalRegulations (CFR).

In certain embodiments, the biologically active agent is a peptide.According to the present invention, a “peptide” or “protein” comprises astring of at least two amino acids linked together by peptide bonds. Theterms “protein” and “peptide” may be used interchangeably. Peptide mayrefer to an individual peptide or a collection of peptides. Peptides maycontain natural amino acids and/or non-natural amino acids (i.e.,compounds that do not occur in nature but that can be incorporated intoa polypeptide chain) and/or amino acid analogs, as are known in the art.Exemplary peptides include GCGGGRGDSPG (RGD), GCGGGVPHSRNSG (PHSRN),GCGGGYIGSRG (YIGSR), growth factors, and the like. One or more of theamino acids in a peptide may be modified, for example, by the additionof a chemical entity such as a carbohydrate group, a phosphate group, afarnesyl group, an isofarnesyl group, a fatty acid group, a linker forconjugation, functionalization, by the addition of a biologically activeagent, or by other structural modifications. In certain embodiments,structural modifications of a peptide lead to a more stable peptide(e.g., greater half-life in vivo). Other structural modifications mayinclude cyclization of the peptide, incorporation of D-amino acids, etc.None of the modifications should substantially interfere with thedesired biological activity of the peptide.

In certain embodiments, the biologically active agent is apolynucleotide (e.g., a polymer of nucleotides). A polynucleotidecomprises at least three nucleotides. The polymer may include naturalnucleosides (i.e., adenosine, thymidine, guanosine, cytidine, uridine,deoxyadenosine, deoxythymidine, deoxyguanosine, and deoxycytidine),nucleoside analogs (e.g., 2-aminoadenosine, 2-thiothymidine, inosine,pyrrolo-pyrimidine, 3-methyl adenosine, C5-propynylcytidine,C5-propynyluridine, C5-bromouridine, C5-fluorouridine, C5-iodouridine,C5-methylcytidine, 7-deazadenosine, 7-deazaguanosine, 8-oxoadenosine,8-oxoguanosine, O(6)-methylguanine, and 2-thiocytidine), chemicallymodified bases, biologically modified bases (e.g., methylated bases),intercalated bases, modified sugars (e.g., 2′-fluororibose, ribose,2′-deoxyribose, arabinose, and hexose), or modified phosphate groups(e.g., phosphorothioates and 5′-N-phosphoramidite linkages).

In certain embodiments, the biologically active agent is modified with alinker group in order to facilitate attachment to an inventive polymer.In certain embodiments, the biologically active agent is modified with anucleophilic or electrophilic group in order to facilitate attachment toan inventive polymer. For example, in certain embodiments, thebiologically active agent is modified with an amino acid (or a peptidecontaining an amino acid modified with a biologically active agent)which bears a nucleophilic thiol, nucleophilic hydroxyl, or nucleophilic—NH— moiety (e.g., the amino acids cysteine, tyrosine, histidine,tryptophan, serine, threonine and lysine as depicted in FIG. 32; whereinR^(AA) is a suitable carboxylic acid protecting group, as definedherein, or is a different, yet suitable group, such as an amino acid orpeptide chain). The nucleophilic moiety of the amino acid (modified witha biologically active agent) may facilitate covalent attachment via itsaddition to an electrophilic group present on the inventive polymer, ordisplacement of a suitable leaving group. Electrophilic groups presenton the inventive polymer include, for example, oxo group (═O), thiooxogroup (═S), acrylate groups a double bond, a triple bond, a carboxylicacid moiety (—CO₂H), a —CHO group, an ester group, an activatedcarboxylic acid moiety (as defined herein), and the like. Suitableleaving groups present on the inventive polymer include, for example, ahalogen, a hydroxyl moiety, an activated hydroxyl moiety (as definedherein), and the like. Alternatively, an electrophilic moiety of theamino acid, such as the carboxylic acid moiety of the amino acid, mayfacilitate covalent attachment via reaction with a nucleophilic grouppresent on the inventive polymer.

Pharmaceutical Compositions and Formulations

The present invention provides a pharmaceutical composition comprisingan inventive polymer. In certain embodiments, the pharmaceuticalcomposition further comprises a biologically active agent, as describedherein. In certain embodiments, the pharmaceutical composition includesany number of additional biologically active agents, for example, asecond, a third, a fourth, or a fifth, biologically active agent.

In certain embodiments, the pharmaceutical composition further comprisesa pharmaceutically acceptable carrier, adjuvant, or vehicle, which, asused herein, includes any and all solvents, diluents, or other liquidvehicle, dispersion or suspension aids, surface active agents, isotonicagents, thickening or emulsifying agents, preservatives, solid binders,lubricants and the like, as suited to the particular dosage formdesired. Remington's Pharmaceutical Sciences, Sixteenth Edition, E. W.Martin (Mack Publishing Co., Easton, Pa., 1980) discloses variouscarriers used in formulating pharmaceutically acceptable compositionsand known techniques for the preparation thereof. Except insofar as anyconventional carrier medium is incompatible with the polymer of thepresent invention, such as by producing any undesirable biologicaleffect or otherwise interacting in a deleterious manner with any othercomponent(s) of the pharmaceutically acceptable composition, its use iscontemplated to be within the scope of this invention.

Some examples of materials which can serve as pharmaceuticallyacceptable carriers include, but are not limited to, ion exchangers,alumina, aluminum stearate, lecithin, triethyl citrate, serum proteins,such as human serum albumin, buffer substances such as phosphates,glycine, sorbic acid, or potassium sorbate, partial glyceride mixturesof saturated vegetable fatty acids, water, salts or electrolytes, suchas protamine sulfate, disodium hydrogen phosphate, potassium hydrogenphosphate, sodium chloride, zinc salts, colloidal silica, magnesiumtrisilicate, polyvinyl pyrrolidone, polyacrylates, waxes,polyethylene-polyoxypropylene-block polymers, wool fat, sugars such aslactose, glucose and sucrose; starches such as corn starch and potatostarch; cellulose and its derivatives such as sodium carboxymethylcellulose, microcrystalline cellulose, ethyl cellulose and celluloseacetate; powdered tragacanth; malt; gelatin; hypromellose (vegetarianversion of gelatin); talc; excipients such as cocoa butter andsuppository waxes; oils such as peanut oil, cottonseed oil; saffloweroil; sesame oil; olive oil; corn oil and soybean oil; glycols; such apropylene glycol or polyethylene glycol; esters such as ethyl oleate andethyl laurate; agar; buffering agents such as sodium hydroxide,magnesium hydroxide and aluminum hydroxide; alginic acid; pyrogen-freewater; isotonic saline; Ringer's solution; ethyl alcohol, and phosphatebuffer solutions; inorganic or organic salts such as sodium chloride,sodium hydrogen phosphate, sodium nitrate and sodium acetate, or acidsand salts such as tartaric, citric or succinic acid; sugars, e.g.mannitol, glucose, fructose, lactose and dextran compounds; as well asother non-toxic compatible lubricants such as sodium lauryl sulfate andmagnesium stearate, as well as coloring agents, releasing agents,coating agents, sweetening, flavoring and perfuming agents,preservatives and antioxidants can also be present in the composition.

Uses of the Inventive Polymers

The inventive polymers may be useful in drug delivery (e.g., delivery ofantibiotics, drugs, bioactive agents); as an injectable drug deliverysystem for mechanically taxing environments (such as within joints)where the material may release a drug in a controlled manner withoutbeing compromised by a dynamic or static external environment; aschewing gum for delivering biologically active materials and/ornutrients and/or vitamins); as an I.V. infusion material for patientsrequiring an osmotic active agent to reduce brain oedema, to reduceswelling of any other kind of tissue or organ, and/or for patientsrequiring colloid volume expansion; as a hydrogel used forcell-encapsulation; as long term circulating particles for applicationsincluding targeted drug delivery, blood substitutes; patches fordiabetic ulcers; intra-abdominal implant to prevent adhesions; in vivoand in vitro sensors; as edible films (e.g., for taking a medication);fiber optics (e.g., provide a porous network for delivering fluids invivo); intraocular devices; in formation of nerve conduits; in meshrepair of herniae (e.g., abdominal herniae); in ligament repair; asosteo-synthesis material (e.g., screws); in intervertebral disc repair;in soft tissue repair; in bone tissue repair; in heart valvereplacement; in osmotically active infusions; use of biodegradableparticles, tubes, spheres, strands, threads, coiled strands, films,sheets, fibers, meshes, and the like; as catheters, intravenous (IV)lines, feeding tubes, O-rings, septa, and the like; in sutures (tunablefor fast or slow degradation); in surgical glue and adhesives; inpost-trauma surgery adhesion prevention; as components of contactlenses; for medical implant coatings (e.g., stents); for injectables;for vascular grafts; microfabrication applications (capillary networks,diagnostics) for tissue engineering (i.e., bladder, bone, brain, nerve,skin, cardiac tissue, ligament, cartilage, tendon, genital, muscle,artery, veins, kidney, pancreas, liver, intestine, stomach, and othertissues); and as an injectable (e.g., to aid in cosmetic and/or surgicalprocedures). In the industrial field, the inventive biodegradablepolymers may be useful in the fields of agriculture and landscaping(e.g., seeding strips and tapes); biodegradable packaging (e.g., foodcontainers; gift wrappings; foams; filters; disposable bags);biodegradable outdoor items (e.g., as a core material of balls such asgolf balls, baseballs, and bouncing balls; as a material for inflatableballoons; as a ski or board wax; as a material for fishing lures); as acomponent in cosmetics (e.g., as an alternative hair product to waxproducts; as an injectable for cosmetic surgery); as a material inabsorbent garments (e.g., disposable diapers; panty liners; incontinenceprotectors); edible films (e.g., protection of freshness of food productand be completely biodegradable within the digestive tract; flavorand/or aroma barriers); and as a material in food formulations (e.g.,diet formulations). The present invention contemplates, but is notlimited to, all such useful applications for polymers of the presentlyclaimed invention.

Methods of Using an Inventive Polymer

The present invention provides a method of using an inventive polymer ora polymer composition, as described above and herein, comprisingadministering to a subject suffering from a disease, condition, ordisorder an inventive polymer or polymer composition.

In certain embodiments, a therapeutically effective amount of theinventive polymer or composition is administered. As used herein, a“therapeutically effective amount” of an inventive polymer orcomposition is an amount that can achieve a desired therapeutic and/orprophylactic effect. A “therapeutically effective amount” is at least aminimal amount of an inventive polymer or composition which issufficient for preventing, ameliorating, reducing, delaying, ordiminishing severity of a disease, disorder, or condition from which asubject is suffering.

Exemplary diseases, conditions, or disorders which may be treatable bythe polymers or pharmaceutical compositions of the present inventioninclude: anxiety, convulsions or epilepsy, depression, pain, bacterialinfections, viral infections, fungal infections, hormonal imbalances,chemical imbalances, allergic disorders or conditions, external orinternal lesions, diseased tissue, bone or muscle injuries, bonebreakage or fracture, joint conditions, arthritis, sepsis, necrosis,autoimmune diseases, blood disorders, bone disorders, cancers,circulation diseases, dental conditions, digestion and nutritiondisorders, gastrointestinal diseases, genetic disorders, heart diseases,hormonal disorders, infectious diseases, inflammation, kidney diseases,liver diseases, mental health disorders, metabolic diseases,neurological disorders, skin conditions, and the like.

In certain embodiments, the inventive polymer, or pharmaceuticalcomposition comprising the inventive polymer, is administered to thesubject by any known means, e.g., transdermally, orally, per anum,parenterally, intravenously (IV), intra-arterially, subcutaneously,intracutaneously, intradural, subdural, epidural, by surgicallyimplantation, absorption, ingestion, injection, or inhalation of theinventive polymer or pharmaceutical composition.

In certain embodiments, the inventive polymer is a component of abiomedical device or implant. In certain embodiments, the inventivepolymer is a polymer film or coating on an implant. In certainembodiments, the inventive polymer is an implant. In certainembodiments, the inventive polymer implant is a polymer matrix.

In certain embodiments, the inventive polymer is injected or implantedinto a subject. In certain embodiments, the pre-polymer to the inventivepolymer (i.e., prior to polymerization) is injected or implanted into asubject. In certain embodiments, the pre-polymer is injected orsurgically implanted, and polymerized in vivo.

In one embodiment, the inventive polymer is surgically implanted orinjected into a subject on or near diseased or damaged tissue. Incertain embodiments, the inventive polymer implant aids in the in-growthof surrounding healthy tissue to the diseased area.

In certain embodiments, the inventive polymer further includes abiologically active agent. Biologically active agents include anysubstance used as a medicine for treatment, prevention, delay, reductionor amelioration of a disease, condition, or disorder, and refers to asubstance that is useful for therapy, including prophylactic andtherapeutic treatment. A biologically active agent also includes acompound that increases the effect or effectiveness of another compound,for example, by enhancing potency or reducing adverse effects of theother compound.

In certain embodiments, the biologically active agent is cleaved fromthe inventive polymer upon enzymatic hydrolysis. In certain embodiments,the biologically active agent, upon release or cleavage, participates intreating a condition, disease, or disorder from which a subject issuffering.

Methods of Making an Inventive Polymer

The present invention provides a method of making an inventive polymercomprising the steps of:

(i) providing a polyol;

(ii) providing a polycarboxylic acid, or derivative thereof; and

(iii) reacting the polyol with the polycarboxylic acid to provide theinventive polymer.

In certain embodiments, the inventive polymer, so provided, is a waterinsoluble polymer. In certain embodiments, the inventive polymer, soprovided, is a water soluble polymer. The polyol and polycarboxylic acidof step (i) and (ii) may be any polyol and polycarboxylic acid sodescribed above and herein; thus the inventive polymer formed from theabove method may be any combination or ratio of polyol to polycarboxylicacid, as described above and herein.

One of ordinary skill in the art will appreciate that a wide variety ofreaction conditions may be employed to promote the above transformation,therefore, a wide variety of reaction conditions are envisioned; seegenerally, March's Advanced Organic Chemistry: Reactions, Mechanisms,and Structure, M. B. Smith and J. March, 5^(th) Edition, John Wiley &Sons, 2001, and Comprehensive Organic Transformations, R. C. Larock,2^(nd) Edition, John Wiley & Sons, 1999, the entirety of both of whichare incorporated herein by reference.

In certain embodiments, the reaction of step (iii) is a condensationreaction (e.g., reaction between a carboxylic acid or derivative thereofand an alcohol, with the extrusion of water, an alcohol by-product, or asuitable leaving group). In certain embodiments, the condensationreaction of step (iii) employs Schotten-Baumann reaction conditions. TheSchotten-Baumann reaction is a well-known reaction to those skilled inthe art; see generally Sonntag et al., Chem. Rev. (1953) 52:237-4161,and Challis and Butler, Chem. Amino Group (1968) 277-347, the entiretyof both of which are incorporated herein by reference.

In certain embodiments, the reaction of step (iii) further comprises theapplication of heat. In certain embodiments, the reaction of step (iii)comprises heating the polyol and the polycarboxylic acid to atemperature of at least 50° C. In certain embodiments, the reaction isheated to a temperature of at least 60° C., 70° C., 80° C., 90° C., 100°C., 110° C., 120° C., 125° C., 130° C., 135° C., 140° C., 145° C., 150°C., 155° C., 160° C., 165° C., or 170° C.

In certain embodiments, the reaction of step (iii) further comprisesconducting the reaction under reduced pressure (i.e., in a vacuum, invacuo).

In certain embodiments, the condensation reaction of step (iii) furtherincludes an activating agent. Exemplary activating agents include, butare not limited to, thionyl chloride, thionyl bromide, oxalyl chloride,Bronstead acids, and Lewis acids. Exemplary Bronstead acids include, butare not limited to, hydrogen chloride, hydrogen bromide, acetic acid,formic acid, and the like. Exemplary Lewis acids include, but are notlimited to, aluminum chloride, iron chloride, boron trifluoride, borontribromide, and boron trichloride.

In certain embodiments, the reaction of step (iii) further includes asuitable solvent. However, in certain embodiments, the reaction of step(iii) does not include a solvent.

A “suitable solvent” is a solvent that, in combination with the combinedreacting partners and reagents, facilitates the progress of the reactionthere-between. A suitable solvent may solubilize one or more of thereaction components, or, alternatively, the suitable solvent mayfacilitate the suspension of one or more of the reaction components;see, generally, March (2001). Suitable solvents include ethers,halogenated hydrocarbons, aromatic solvents, polar aprotic solvents,polar protic solvents, or mixtures thereof. In certain embodiments, thesolvent comprises water, diethyl ether, dioxane, tetrahydrofuran (THF),dichloromethane (DCM), dichloroethane (DCE), chloroform, toluene,benzene, dimethylformamide (DMF), dimethylacetamide (DMA),dimethylsulfoxide (DMSO), N-methylpyrrolidinone (NMP), or mixturesthereof.

In certain embodiments, the polyol is a fully unprotected polyol (i.e.,comprising free, unprotected, —OH groups). In certain embodiments, thepolycarboxylic acid is a fully unprotected polycarboxylic acid (i.e.,comprising free, unprotected, —COOH groups). In certain embodiments,both the polyol and the polycarboxylic acid are fully unprotected.

In certain embodiments, the polycarboxylic acid is an activated or aprotected polycarboxylic acid. Activated carboxylic acids are well knownto one skilled in the art. Exemplary activated carboxylic acids include,but are not limited to, carboxylic acids activated as anhydrides or asacyl halides (e.g., acyl chloride, acyl bromide). Exemplary protectedcarboxylic acids, such as esters, are also well known to one skilled inthe art; see generally, Greene (1999). Suitable carboxylic acidprotecting groups include, but are not limited to, silyl-, alkyl-,alkenyl-, aryl-, and arylalkyl-protected carboxylic acids. Examples ofsuitable silyl groups include trimethylsilyl, triethylsilyl,t-butyldimethylsilyl, t-butyldiphenylsilyl, triisopropylsilyl, and thelike. Examples of suitable alkyl groups include methyl, ethyl, n-propyl,isopropyl, allyl, n-butyl, sec-butyl, or t-butyl group, benzyl,p-methoxybenzyl, 3,4-dimethoxybenzyl, trityl, t-butyl,tetrahydropyran-2-yl. Examples of suitable alkenyl groups include allyl.Examples of suitable aryl groups include optionally substituted phenyl,biphenyl, or naphthyl. Examples of suitable arylalkyl groups includeoptionally substituted benzyl (e.g., p-methoxybenzyl (MPM),3,4-dimethoxybenzyl, O-nitrobenzyl, p-nitrobenzyl, p-halobenzyl,2,6-dichlorobenzyl, p-cyanobenzyl), and 2- and 4-picolyl.

In certain embodiments, for example, when the polycarboxylic acid is aprotected polycarboxylic acid, the reaction of step (iii) may furthercomprise a base. Exemplary bases include potassium carbonate, potassiumhydroxide, sodium hydroxide, tetrabutylammonium hydroxide,benzyltrimethylammonium hydroxide, triethylbenzylammonium hydroxide,1,1,3,3-tetramethylguanidine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),N-methylmorpholine, diisopropylethylamine (DIPEA),tetramethylethylenediamine, pyridine, N,N-dimethylamino pyridine (DMAP),or triethylamine.

In certain embodiments, the product of step (iii) is a hydrogel. Incertain embodiments, the product of step (iii) is a tough elastomer. Incertain embodiments, the product of step (iii) is a hydrated elastomer.In certain embodiments, the product of step (iii) is a stiff, hardpolymer.

In certain embodiments, the product of step (iii) is water-soluble. Incertain embodiments, when the product of step (iii) is water-soluble,the polyol of step (i) is also water-soluble. In certain embodiments,when the product of step (iii) is water-soluble, the polycarboxylic acidof step (ii) is also water soluble. In certain embodiments, when productof step (iii) is water-soluble, both the polyol of step (i) and thepolycarboxylic acid are water-soluble. In certain embodiments, thewater-soluble product of step (iii) is also a hydrogel or a hydratedelastomer.

In certain embodiments, the product of step (iii) is not water-soluble.In certain embodiments, when the product of step (iii) iswater-insoluble, the polyol of step (i) is also embodiments, the polyolis xylitol, mannitol, sorbitol, or maltitol. In certain embodiments, thepolyol is xylitol. In certain embodiments, the sugar alcohol glycerol isspecifically excluded.

Similarly, in certain aspects of the present invention, thepolycarboxylic acid monomer used in the formation of the inventivepolymer is a compound found in nature, or derived from nature. Incertain embodiments, the polycarboxylic acid is endogenous to the humanmetabolic system. In certain embodiments, the polycarboxylic acid isnon-toxic. In certain embodiments, the polycarboxylic acid is analiphatic polycarboxylic acid (i.e., does not contain arylene orheteroarylene groups). In certain embodiments, the polycarboxylic acidis optically enriched. In certain embodiments, the polycarboxylic acidhas a center of symmetry.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer is a dicarboxylic acid. In certain embodiments,the polycarboxylic acid is a tricarboxylic acid.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer is an amino acid. Exemplary amino acids includeaspartic acid or glutamic acid.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer is a polypeptide. In certain embodiments, thepolycarboxylic acid used in the formation of the inventive polymer is anoligopeptide. In certain embodiments, the polycarboxylic acid used inthe formation of the inventive polymer is a protein.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer is a metabolite. In certain embodiments, themetabolite is a citric acid cycle (Kreb's cycle) metabolite. Exemplarymetabolites include succinic acid, fumaric acid, α-ketoglutaric acid,oxaloacetic acid, malic acid, oxalosuccinic acid, isocitric acid,cis-aconitic acid, and citric acid. In certain embodiments, thepolycarboxylic acid is optionally substituted citric acid. However, incertain embodiments, citric acid is specifically excluded. Furthermore,in certain embodiments, the polymer formed from citric acid and thepolyol glycerol is specifically excluded.

In certain embodiments, the polycarboxylic acid used in the formation ofthe inventive polymer comprises an optionally substituted aldaric acid.An aldaric acid (a “sugar acid”) is an oxidized aldose sugar in whichboth the hydroxyl functional groups of the terminal carbon and thealdehyde function of the first carbon have been fully oxidized tocarboxylic acid water-insoluble. In certain embodiments, when theproduct of step (iii) is water-insoluble, the polycarboxylic acid ofstep (ii) is also water-insoluble. In certain embodiments, when productof step (iii) is water-insoluble, both the polyol of step (i) and thepolycarboxylic acid are water-insoluble. In certain embodiments, thewater-insoluble product of step (iii) is also a tough elastomer or ahydrated elastomer.

Step (iv): Functionalization of the Polymer of Step (iii)

(I). Acrylation

The method of making an inventive polymer may further comprise the stepof:

(iv) reacting the polymer of step (iii) with a acrylating compound.

Reaction of the polymer of step (iii) with an acrylating compound instep (iv) provides an acrylated polymer. One of ordinary skill in theart will appreciate that a wide variety of reaction conditions may beemployed to promote acrylation of the polymer of step (iii) with anacrylating compound, therefore, a wide variety of reaction conditionsare envisioned; see generally, March's Advanced Organic Chemistry:Reactions, Mechanisms, and Structure, M. B. Smith and J. March, 5^(th)Edition, John Wiley & Sons, 2001, and Comprehensive OrganicTransformations, R. C. Larock, 2^(nd) Edition, John Wiley & Sons, 1999;the entirety of both of which are incorporated herein by reference.

Exemplary acrylating compounds include, but are not limited to, acrylicacid, acryloyl chloride, methacrylic acid, methacryloyl chloride,but-2-enoic acid, but-2-enoyl chloride, butyl acrylate, 2-ethylhexylacrylate, methyl acrylate, ethyl acrylate, methyl methacrylate,methacrylic anhydride, allyl glycidyl ether, glycidyl acrylate, glycidylmethacrylate, trimethylol propane triacrylate (TMPTA), and the like.

Additional reagents and/or conditions may be employed to facilitate theacrylation reaction of step (iv) between acrylating compound and thepolymer, such as, for example, the employment of a suitable base, or theapplication of heat.

In certain embodiments, the acrylation reaction of step (iv) furthercomprises the application of heat. In certain embodiments, the reactionof step (iv) comprises heating the acrylating compound and the polymerto a temperature of at least 30° C. In certain embodiments, the reactionis heated to a temperature of at least 40° C., 50° C., 60° C., 70° C.,80° C., 90° C., or 100° C.

However, in certain embodiments, the acrylation reaction of step (iv)further comprises cooling. In certain embodiments, the reaction of step(iv) comprises cooling the acrylating compound and the polymer to atemperature of at least 10° C. In certain embodiments, the reaction iscooled to a temperature of at least 5° C. or 0° C. In certainembodiments, the reaction is cooled to a temperature of at least 5° C.,and then gradually warmed to room temperature.

In certain embodiments, the acrylation reaction of step (iv) furthercomprises a suitable base. Exemplary bases include potassium carbonate,potassium hydroxide, sodium hydroxide, tetrabutylammonium hydroxide,benzyltrimethylammonium hydroxide, triethylbenzylammonium hydroxide,1,1,3,3-tetramethylguanidine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),N-methylmorpholine, diisopropylethylamine (DIPEA),tetramethylethylenediamine, pyridine, N,N-dimethylamino pyridine (DMAP),or triethylamine.

In certain embodiments, the reaction of step (iv) further comprises asuitable solvent. Suitable solvents include ethers, halogenatedhydrocarbons, aromatic solvents, polar aprotic solvents, or mixturesthereof. In certain embodiments, the solvent comprises diethyl ether,dioxane, tetrahydrofuran (THF), dichloromethane (DCM), dichloroethane(DCE), chloroform, toluene, benzene, dimethylformamide (DMF),dimethylacetamide (DMA), dimethylsulfoxide (DMSO), N-methylpyrrolidinone(NMP), or mixtures thereof.

In certain embodiments, the polymer product of the acrylation reactionof step (iv) is water-soluble. In certain embodiments, the polymerproduct of either the acrylation reaction step is not water-soluble. Incertain embodiments, the polymer product of the acrylation reaction ofstep (iv) is a hydrogel. In certain embodiments, the polymer product ofthe acrylation reaction of step (iv) is a tough elastomer. In certainembodiments, the polymer product of the acrylation reaction of step (iv)is a hydrated elastomer.

In certain embodiments, the polymer product of the acrylation reactionof step (iv) is isolated by extraction with an organic solvent. Incertain embodiments, the polymer product of the acrylation reaction ofstep (iv) is precipitated from the reaction. In certain embodiments, thepolymer product of the acrylation reaction of step (iv) is isolated viafiltration. In certain embodiments, the polymer product of theacrylation reaction of step (iv) is further dialysed against water. Incertain embodiments, the polymer product of the acrylation reaction ofstep (iv) is further dialysed against water and then lyophilized.

(II). Dihydrazide Chemistry

Alternatively, in certain embodiments, the reaction of step (iv) maycomprise the step of:

(iv) reacting the polymer of step (iii) with a dihydrazide compound.

In certain embodiments, the polymer of step (iii) which has a carboxylicacid, ester, or aldehydic functional group is treated with a dihydrazidecompound to provide a hydrazide modified polymer. In certainembodiments, the polymer of step (iii) is first modified by activatingthe carboxylic acid, ester, or aldehydic functional group present on thepolymer, and then treating this polymer having an activated functionalgroup with a dihydrazide compound to provide a hydrazide modifiedpolymer.

For example, in certain embodiments, the polymer of step (iii) havingcarboxylic acid groups (—CO₂H) is further modified by reacting the —CO₂Hgroups of the polymer with a dihydrazide compound to provide a hydrazidemodified polymer. In certain embodiments, the carboxylic acid groups areactivated. In certain embodiments, the carboxylic acid groups areactivated with an activating reagent prior to treatment with thedihydrazide compound.

Exemplary activating reagents include, but are not limited to, thionylchloride, thionyl bromide, oxalyl chloride, which generate the an acylhalide as the activated carboxylic acid. Other activating reagents arecommonly referred to as “coupling reagents” (for example,benzotriazol-1-yloxy-tris(dimethylamino)-phosphonium hexafluorophosphate(BOP), benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphoniumhexafluorophosphate (PyBOP), bromo-tris-pyrrolidino phosphoniumhexafluorophosphate (PyBroP), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), N,N′-carbonyldiimidazole (CDI),3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT),1-hydroxy-7-azabenzotriazole (HOAt), 1-hydroxy-7-benzotriazole (HOBt),2-(7-aza-1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluroniumhexafluorophosphate (HATU),2-(6-chloro-1H-benzotriazole-1-yl)-1,1,3,3-tetramethylaminiumhexafluorophosphate (HCTU),2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate(HBTU), O-(7-azabenzotriazole-1-yl)-N,N,N′,N′-tetramethyluroniumtetrafluoroborate (TATU),2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate(TBTU),N,N,N′,N′-tetramethyl-O-(3,4-dihydro-4-oxo-1,2,3-benzotriazin-3-yl)uraniumtetrafluoroborate (TDBTU), and O—(N-succinimidyl)-1,1,3,3-tetramethyluranium tetrafluoroborate (TSTU)). Other exemplary activated carboxylicacids include, but are not limited to, esters, anhydrides, and —CO₂—(sulfonyl) groups. Sulfonyl groups include trifluoromethylsulfonyl(-Tf), tolylsulfonyl (-Ts), methanesulfonyl (-Ms),(4-nitrophenylsulfonyl) (-Nos), and (2-nitrophenylsulfonyl) (-Ns).

In certain embodiments, the polymer of step (iii) having an aldehydicgroup (—CHO) is further modified by reacting the —CHO group of thepolymer with a dihydrazide compound to provide a hydrazide modifiedpolymer.

One of ordinary skill in the art will appreciate that a wide variety ofreaction conditions may be employed to promote the reaction between acarboxylic acid and a dihydrazide compound, or an aldehyde and adihydrazide compound, and therefore, a wide variety of reactionconditions are envisioned; see generally, Bulpitt and Aeschlimann, J.Biomed. Mater. Re. (1999) 47:152-169; March's Advanced OrganicChemistry: Reactions, Mechanisms, and Structure, M. B. Smith and J.March, 5^(th) Edition, John Wiley & Sons, 2001, and ComprehensiveOrganic Transformations, R. C. Larock, 2^(nd) Edition, John Wiley &Sons, 1999; the entirety of which are incorporated herein by reference.

Exemplary dihydrazide compounds include, but are not limited to, adipicdihydrazide, succinic dihydrazide, carbonic dihydrazide, oxalicdihydrazide, glutaric dihydrazide, pimelic dihydrazide, malonicdihydrazide, maleic dihydrazide, and isophthalic dihydrazide.

Additional reagents and/or conditions may be employed to facilitate thereaction between the dihydrazide compound and the —CHO or —CO₂Hfunctionalized polymer, such as, for example, the employment of asuitable base, a suitable activating reagent, or the application ofheat.

In certain embodiments, the reaction between the dihydrazide compoundand the —CHO or —CO₂H functionalized polymer further comprises theapplication of heat. In certain embodiments, the reaction comprisesheating the dihydrazide compound and the polymer to a temperature of atleast 30° C. In certain embodiments, the reaction is heated to atemperature of at least 40° C., 50° C., 60° C., 70° C., 80° C., 90° C.,or 100° C.

However, in certain embodiments, the reaction between the dihydrazidecompound and the —CHO or —CO₂H functionalized polymer further comprisescooling. In certain embodiments, the reaction comprises cooling thedihydrazide compound and the polymer to a temperature of at least 10° C.In certain embodiments, the reaction is cooled to a temperature of atleast 5° C. or 0° C. In certain embodiments, the reaction is cooled to atemperature of at least 5° C., and then gradually warmed to roomtemperature.

In certain embodiments, the reaction between the dihydrazide compoundand the —CHO or —CO₂H functionalized polymer further comprises asuitable base. Exemplary bases include potassium carbonate, potassiumhydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide,tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide,triethylbenzylammonium hydroxide, 1,1,3,3-tetramethylguanidine,1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), N-methylmorpholine,diisopropylethylamine (DIPEA), tetramethylethylenediamine, pyridine,N,N-dimethylamino pyridine (DMAP), or triethylamine.

In certain embodiments, the reaction between the dihydrazide compoundand the —CHO or —CO₂H functionalized polymer further comprises asuitable solvent. Suitable solvents include water, ethers, halogenatedhydrocarbons, aromatic solvents, polar aprotic solvents, polar proticsolvents, or mixtures thereof. In certain embodiments, the solventcomprises water, saline, diethyl ether, dioxane, tetrahydrofuran (THF),dichloromethane (DCM), dichloroethane (DCE), chloroform, toluene,benzene, dimethylformamide (DMF), dimethylacetamide (DMA),dimethylsulfoxide (DMSO), N-methylpyrrolidinone (NMP), or mixturesthereof.

In certain embodiments, the hydrazide modified polymer of step (iv) iswater-soluble. In certain embodiments, the hydrazide modified polymer ofstep (iv) is not water-soluble. In certain embodiments, the hydrazidemodified polymer of step (iv) is a hydrogel. In certain embodiments, thehydrazide modified polymer of step (iv) is a tough elastomer. In certainembodiments, the hydrazide modified polymer of step (iv) is a hydratedelastomer.

In certain embodiments, the hydrazide modified polymer of step (iv) isisolated by extraction with an organic solvent. In certain embodiments,the hydrazide modified polymer of step (iv) is precipitated from thereaction. In certain embodiments, the hydrazide modified polymer of step(iv) is isolated via filtration. In certain embodiments, the hydrazidemodified polymer of step (iv) is further dialysed against water. Incertain embodiments, the hydrazide modified polymer of step (iv) isfurther dialysed against water and then lyophilized.

(III) Oxidation

Alternatively, in certain embodiments, the reaction of step (iv) maycomprise the step of:

-   -   (iv) oxidizing the polymer of step (iii).

Furthermore, in certain embodiments, the reaction of step (iv) maycomprise the step of:

(iv) oxidizing the polymer of step (iii) to provide an oxidized product,and reacting the oxidized product with a dihydrazide compound to providea hydrazide product.

In certain embodiments, the oxidation reaction of step (iv) may compriseoxidizing the polymer of step (iii) with a suitable oxidizing reagent.Suitable oxidation reagents include chromium oxidation reagents, leadoxidation reagents, iron oxidation reagents, copper oxidation reagents,mercury oxidation reagents, vanadium oxidation reagents, nickeloxidation reagents, ruthenium oxidation reagents, magnesium oxidationreagents, manganese oxidation reagents, osmium oxidation reagents,peroxides, periodate oxidation reagents, iodine oxidation reagents,chloride oxidation reagents, oxygen, O₃, or mixtures thereof. Exemplaryoxidation reagents include, but are not limited to, Ca(OCl₂), MnO₂,KMnO₄, BaMnO₄, Cu(MnO₄)₂, NaMnO₄, HgO, Pb(OAc)₂, NaOCl, NiO₂, RuO₄,K₂FeO₄, VO(acac)₂, OsO₄, KIO₄, NaIO₄, K₂RuO₄, PhIO, PhI(OAc)₂, K₂Cr₂O₇,Collins reagent (CrO₃-2pyridine), pyridinium dichromate (PDC), andpyridinium chlorochromate (PCC).

One of ordinary skill in the art will appreciate that a wide variety ofreaction conditions may be employed to promote oxidation of the polymerof step (iv) with an oxidizing reagent, therefore, a wide variety ofreaction conditions are envisioned; see generally, March's AdvancedOrganic Chemistry: Reactions, Mechanisms, and Structure, M. B. Smith andJ. March, 5^(th) Edition, John Wiley & Sons, 2001, and ComprehensiveOrganic Transformations, R. C. Larock, 2^(nd) Edition, John Wiley &Sons, 1999; the entirety of both of which are incorporated herein byreference. For example, in certain embodiments, the oxidizing reagent isa reagent which oxidizes a hydroxyl group to an aldehyde. In certainembodiments, the oxidizing reagent is a reagent which cleaves a diol toprovide an aldehydic moiety (—CHO).

Additional reagents and/or conditions may be employed to facilitate theoxidation reaction between an oxidizing reagent and the polymer of step(iii), such as, for example, the employment of a suitable base, or theapplication of heat.

In certain embodiments, the oxidation reaction of step (iv) furthercomprises the application of heat. In certain embodiments, the oxidationreaction of step (iv) comprises heating the oxidizing reagent and thepolymer to a temperature of at least 30° C. In certain embodiments, theoxidation reaction is heated to a temperature of at least 40° C., 50°C., 60° C., 70° C., 80° C., 90° C., or 100° C.

However, in certain embodiments, the oxidation reaction of step (iv)further comprises cooling. In certain embodiments, the oxidationreaction of step (iv) comprises cooling the oxidizing reagent and thepolymer to a temperature of at least 10° C. In certain embodiments, theoxidation reaction is cooled to a temperature of at least 5° C. or 0° C.In certain embodiments, the oxidation reaction is cooled to atemperature of at least 5° C., and then gradually warmed to roomtemperature.

In certain embodiments, the oxidation reaction of step (iv) furthercomprises a suitable base. Exemplary bases include potassium carbonate,potassium hydroxide, sodium hydroxide, lithium hydroxide, potassiumhydroxide, tetrabutylammonium hydroxide, benzyltrimethylammoniumhydroxide, triethylbenzylammonium hydroxide,1,1,3,3-tetramethylguanidine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),N-methylmorpholine, diisopropylethylamine (DIPEA),tetramethylethylenediamine, pyridine, N,N-dimethylamino pyridine (DMAP),or triethylamine.

In certain embodiments, the oxidation of step (iv) further comprises asuitable solvent. Suitable solvents include ethers, halogenatedhydrocarbons, aromatic solvents, polar aprotic solvents, polar proticsolvents, or mixtures thereof. In certain embodiments, the solventcomprises water, saline, diethyl ether, dioxane, tetrahydrofuran (THF),dichloromethane (DCM), dichloroethane (DCE), chloroform, toluene,benzene, dimethylformamide (DMF), dimethylacetamide (DMA),dimethylsulfoxide (DMSO), N-methylpyrrolidinone (NMP), or mixturesthereof.

In certain embodiments, the polymer product of the oxidation reaction ofstep (iv), is water-soluble. In certain embodiments, the polymer productoxidation reaction of step (iv) is not water-soluble. In certainembodiments, the polymer product of the oxidation reaction of step (iv)is a hydrogel. In certain embodiments, the polymer product of theoxidation reaction of step (iv) is a tough elastomer. In certainembodiments, the polymer product of the oxidation reaction of step (iv)is a hydrated elastomer.

In certain embodiments, the polymer product of the oxidation reaction ofstep (iv) is isolated by extraction with an organic solvent. In certainembodiments, the polymer product of the oxidation reaction of step (iv)is precipitated from the reaction. In certain embodiments, the polymerproduct of the oxidation reaction of step (iv) is isolated viafiltration. In certain embodiments, the polymer product of the oxidationreaction of step (iv) is further dialysed against water. In certainembodiments, the polymer product of the oxidation reaction of step (iv)is further dialysed against water and then lyophilized.

Step (v): Polymerization

The method of making an inventive polymer may further comprise the stepof:

-   -   (v) polymerizing the product of step (iv).

In certain embodiments, the product of step (iv) is the acrylatedproduct. In certain embodiments, the product of step (iv) is thehydrazide product. In certain embodiments, the product is of step (iv)is the oxidized product.

In certain embodiments, the polymerization reaction is via ring openingmetathesis polymerization (ROMP), reversible addition-fragmentationchain transfer (RAFT) polymerization, reversible addition-fragmentationchain transfer (RAFT) polymerization, or radical polymerization.

In certain embodiments, the radical polymerization is photo-initiated(photopolymerization), light-induced, or heat-induced radicalpolymerization.

In certain embodiments, the polymerization reaction further requiresprior addition of an initiator to the reaction of step (v). Exemplaryinitiators include, but are not limited to, photoinitiators (e.g.,IRGACURE® photoinitiators), peroxides, N-oxides, tert-butyl peroxide,benzoyl peroxide, 2,2-dimethoxy-2-phenyl-acetophenone, acetophenone,azobisisobutyrylnitrile (AIBN), N,N,N′,N′-tetramethylethylenediamine(TEMED), tetraethylenepentamine (TEPA), a Ziegler-Natta catalyst, anacid, a base, a Lewis acid, a Lewis base, a Brønsted acid, or a Brønstedbase.

Alternatively, in certain embodiments, the polymerization reaction is across-linking reaction of the hydrazide modified polymer, and involvesreaction of the hydrazide moiety present in the polymer of step (iv)with a carboxylic acid moeity, or derivative thereof, or an aldehydicmoiety (—CHO) also present in the polymer of step (iv), or in anotherpolymer possessing at least one carboxylic acid moeity, or derivativethereof, or at least one aldehydic moiety (—CHO).

Polymerization/cross-linking of an acrylated polymer or a hydrazidemodified polymer are just two exemplary ways to polymerize/crosslink theinventive polymers. The present invention contemplates many other waysof providing a polymer of step (iii), further modifying the polymer ofstep (iii), and polymerizing/cross-linking the modified polymer toprovide a polymerized/cross-linked product; see generally Hennink andVan Nostrum, Advanced Drug Delivery Reviews 54 (2002) 13-36, theentirety of which is incorporated herein by reference.

In certain embodiments, the reaction of step (v) further comprises asuitable solvent. Suitable solvents include ethers, halogenatedhydrocarbons, aromatic solvents, polar aprotic solvents, polar proticsolvents, or mixtures thereof. In certain embodiments, the solventcomprises water, saline, phosphate-buffered saline (PBS), diethyl ether,dioxane, tetrahydrofuran (THF), dichloromethane (DCM), dichloroethane(DCE), chloroform, toluene, benzene, dimethylformamide (DMF),dimethylacetamide (DMA), dimethylsulfoxide (DMSO), N-methylpyrrolidinone (NMP), or mixtures thereof.

In certain embodiments, the product of step (v) is water-soluble. Incertain embodiments, the product of step (v) is not water-soluble. Incertain embodiments, the product of step (v) is a hydrogel. In certainembodiments, the product of step (v) is a tough elastomer. In certainembodiments, the product of step (v) is a hydrated elastomer.

In certain embodiments, the reaction of step (v) is performed withoutsolvent.

In certain embodiments, the reaction of step (v) is induced in vivo. Incertain embodiments, the reaction of step (v) is induced in vivo byradical polymerization. In certain embodiments, the reaction of step (v)induced in vivo is photo-induced.

Additional Steps and Modifications

The present invention is also directed to a method of making aninventive polymer which includes a biologically active agent. Thebiologically active agent may be incorporated as a polymeric component,either via covalent or non-covalent association, or as an entrapped(e.g., encapsulated) moiety within the polymeric matrix.

Examples of certain modifications to the above method steps which maygenerate a polymer conjugated to a biologically active agent includes,but is not limited to:

(iii) reacting a polyol with a polycarboxylic acid to provide a polymer,and conjugating a polymer to a biologically active agent;

(iv) reacting a polymer of step (iii) with an acrylating compound toprovide an acrylated polymer, and conjugating the acrylated polymer to abiologically active agent;

(iv) reacting a polymer of step (iii) with a dihydrazide compound toprovide an hydrazide modified polymer, and conjugating the hydrazidemodified polymer to a biologically active agent;

(iv) oxidizing a polymer of step (iii) to provide an oxidized polymer,and conjugating an oxidized polymer to a biologically active agent;

(v) polymerizing an acrylated polymer of step (iv) in the presence of abiologically active agent;

(v) cross-linking a hydrazide modified polymer of step (iv) in thepresence of a biologically active agent;

(vi) providing a biologically active agent, and conjugating thebiologically active agent to a polymerized product of step (v);

and/or

(vi) providing a biologically active agent, and conjugating thebiologically active agent to a cross-linked product of step (v).

Any of the above method steps (e.g., acrylation, dihydrazide chemistry,oxidation, polymerization, conjugation to a biologically active agent)may be combined to provide any number of different inventive polymers.Table 3 summarizes the above method steps and exemplary combinationsthereof.

TABLE 3 Step (iii) Step (iv) Step (v) Additional steps 1 polymer 2polymer modification with a biologically active agent 3 polymeracrylation 4 polymer acrylation modification with a biologically activeagent 5 polymer acrylation polymerization 6 polymer acrylationpolymerization modification with a biologically active agent 7 polymeroxidation 8 polymer oxidation reaction with a biologically active agent9 polymer oxidation reaction with a dihydrazide compound 10 polymeroxidation reaction with a reaction with a dihydrazide compoundbiologically active agent 11 polymer reaction with a dihydrazidecompound 12 polymer reaction with a reaction with a dihydrazidebiologically active agent compound 13 polymer reaction with apolymerization dihydrazide compound 14 polymer reaction with apolymerization reaction with a dihydrazide biologically active agentcompound 15 polymer one batch: polymerization of oxidation; the twobatches and other batch: reaction with a dihydrazide compound 16 polymerone batch: polymerization of reaction with a oxidation; the two batchesbiologically active agent and other batch: reaction with a dihydrazidecompound 17 polymer one batch: polymerization of acrylation; the twobatches and other batch: reaction with a dihydrazide compound 18 polymerone batch: polymerization of reaction with a acrylation; the two batchesbiologically active agent and other batch: reaction with a dihydrazidecompound 19 polymer one batch: polymerization of oxidation; the twobatches and other batch: acrylation 20 polymer one batch: polymerizationof reaction with a oxidation; the two batches biologically active agentand other batch: acrylation

The present invention will be more specifically illustrated by thefollowing examples. However, it should be understood that the presentinvention is not limited by these examples in any manner.

EXAMPLES Example 1 Xylitol Based Polymers Biodegradable Waxy Polymers,Hydrogels, and Elastomers

The first step in the synthesis of all pre-polymers includes apolycondensation reaction. Xylitol and the polycarboxylic acid aremelted under an inert atmosphere at a temperature of approximately100-120° C. Then the polycondensation reaction is initiated after 6hours, continuously stirring in vacuo. These thermoplastic pre-polymerscan be divided based on their solubility in water. Water solubleprepolymers can be used as waxy polymer, or further processed intophotocrosslinkable and/or in situ crosslinkable hydrogels. The waterinsoluble pre-polymers can be used as a thermoplastic, waxy polymer, orfurther processed into elastomers, either through polycondensation,photopolymerization, and/or in situ polymerization.

Experiment 1a:

The water soluble pre-polymers are synthesized using xylitol andglutaric acid with a 1:1 molar ratio. The polycondensation was done at100° C., for 5 hours in vacuo, resulting in a colorless, odorless syrup.This first product is also referred to as the water soluble waxypolymer, or poly-xylitol-glutaric acid (PXG 1:1).

Experiment 1b:

The water soluble pre-polymers are synthesized using xylitol and citricacid with a 1:1 molar ratio. The polycondensation was done at 100° C.,for 3 hours in vacuo, resulting in a colorless, glassy thermoplasticpolymer. This first product is referred to as the water soluble polymer,or poly-xylitol-citric acid (PXC 1:1).

Experiment 1c:

The available free hydroxyl and carboxyl groups on the water solublewaxy polymer were functionalized to yield photocrosslinkable and, or insitu crosslinkable hydrogels, using established chemistry. For instance,5 grams of PXG 1:1 is dissolved in N,N-dimethyl formaldehyde (DMF) underanhydrous conditions. 50 mL anhydrous DMF was added to a flame driedround-bottom flask to make a 10% solution (w/v) of polymer. After adding20 mg of DMAP, the reaction flask was placed in an ice bed over astirring plate under nitrogen. Once cooled, “x” mol of acryloyl chloride(the value of “x” varies for any wanted degree of acrylation, whichinfluences biodegradation and mechanical properties of the eventualpolymer) and an equimolar triethylamine was added to start the reaction.The ice-bath was allowed to heat to room temperature overnight. Thissolution was filtered and the acrylated PXG 1:1 (PXGa 1:1) wasprecipitated in a 50:50 ethyl acetate/hexane solution. The precipitatewas allowed to settle at −20° C. overnight and the solvents weredecanted. The PXGa 1:1 was dissolved in PBS, ranging from 50% to 15%v/v, containing 0.5% Irgacure 2399832 photo-initiator. This wasphotopolymerized by exposure to ˜4 mW/cm² ultraviolet light for 10 minusing a longwave ultraviolet lamp (model 100AP, Blak-Ray), resulting invarious hydrogels.

Experiment 1d:

A 1% w/v PXC solution in ddH₂O (200 mL) is filtered through a 0.22micron filter. The molecular weight (MW) of a PXC polymer is around 4kDa, so for a 20-fold excess of methacrylic anhydride, 10 mmol isneeded. On ice and constant stirring, the methacrylic anhydride is addeddrop-wise. Drops in pH are corrected with 5 N NaOH and maintained at apH of 8.0 as much as possible. The reaction is allowed to proceed for 24hrs at 4° C. For purification, the macromers were extensively dialyzedin ddH₂O and the final product methacrylated PXC (PXCma 1:1) wasobtained through freeze-drying. Original description of methacrylationof haluronic acid (HA) provided in Smeds K A and Grinstaff M W. J.Biomed Mater. Res. (2001) 54:115-121.

Experiment 1e.

A photopolymerized hydrogel network of PXCma is obtained by mixing aphotoinitiator (0.05% w/v) and exposure to approximately 4 mW/cm²ultraviolet light for 10 min using a longwave ultraviolet lamp (model100 AP, Blak-Ray).

Experiment 1f.

The carboxyl and hydroxyl groups of the water soluble polymer, PXC 1:1are functionalizable into an in situ crosslinkable hydrogel. Thepreparation of in situ crosslinkable PXC can be done as follows:

Periodate oxidation of PXC to obtain PXC-ALD: 1.0 g PXC (Mw 4 kDa) willbe dissolved in H₂O at a concentration of 10 mg/ml. An aqueous solutionof sodium periodate (0.5 M, 5 ml) will be added dropwise, and thereaction stirred for 2 h at room temperature in the dark. Ethyleneglycol will be then added to inactivate any unreacted periodate. Thereaction was stirred for 1 hour at ambient temperature, and the solutionwas purified by exhaustive dialysis (MWCO 1,000, Spectrapor membrane,Spectrum Laboratories, Rancho Dominguez, Calif.) against ddH₂O for 3days, and the dry product obtained by freeze drying.

Modification of PXC with adipic dihydrazide to obtain PXC-ADH: 0.5 g ofPXC (Mw 4 kDa) will be dissolved in ddH₂O to make a 5 mg/ml solution. Tothis solution will be added a 30-fold molar excess of ADH. The pH of thereaction mixture will be adjusted to 6.8 with 0.1 m NaOH and 0.1 m HCl.0.78 g of EDC (5 mmol) and 0.77 g HOBt (5 mmol) will be dissolved inDMSO/H₂O (1:1 v/v, 5 ml each) and added to the reaction mixture. The pHof the solution will be adjusted to 6.8 and maintained by adding 0.1 NHCl for at least 4 h. The reaction will be allowed to proceed overnight.The pH will be subsequently adjusted to 7.0 and the reaction productsexhaustively dialyzed (MWCO 1,000, SpectraJPor membrane) against H₂O.NaCl will be added to produce a 5% (w/v) solution and PXC-ADH will beprecipitated in chloroform. The precipitate will be re-dissolved in H₂Oand dialyzed again to remove the salt. The purified product will befreeze dried and kept at 4° C.

As depicted in FIGS. 13A-13B, using 1-ethyl-3-[3-dimethylamino)propyl]carbodiimide (EDC) chemistry (steps 1), the carboxylic groups ofthe PXC polymer can be functionalised with amino(dihydrazide) andaldehyde containing groups (steps 2). Using 1-hydroxybenzotriazole(HOBt) to form an easy leaving group and adding adipic dihydrazide tothe reaction mixture, adipic dihydrazide-PXC(PXC-A) can be formed. WithN-hydroxysulfosuccinimide (sulfo-NHS), aminoacetaldehyde dimethylacetal-PXC can be formed which can yield a PXC-aldehyde polymer (step 3)(PXC-B) with a mild acid treatment. The actual hydrogel network isformed when PXC-A and PXC-B are mixed together.

Experiment 2.

Preparation of an in situ crosslinkable PXC hydrogel is done bydissolving the PXC-ADH and PXC-ALD in ddH₂O separately at aconcentration of 20 mg/ml. Gels formed by mixing of solutions asnarrated below.

Experiment 2a.

The water insoluble pre-polymers are synthesized using xylitol andsebacic acid with varying molar ratios. The polycondensation was done at130° C., for 6 hours in vacuo, resulting in a hard, waxy water insolublepolymer. These products are also referred to as the water insoluble waxypolymers, or a 1:1 poly-xylitol-sebacic acid (PXS 1:1) or 1:2poly-xylitol-sebacic acid (PXS 1:2), resembling the molar ratios used.

Experiment 2b.

The water insoluble waxy pre-polymers are melted at 120° C. and pouredon wafers. Subsequently, the polycondensation was continued at 120° C.in vacuo for 3, 4, 7, and 10 days. This further polymerization of PXS1:1 and PXS 1:2 resulted in tough biodegradable elastomers with Young'smoduli ranging from 0.8 to 5.3 MPa.

Experiment 2c.

The available free hydroxyl and carboxyl groups on the water insolublewaxy polymers were functionalized to yield photocrosslinkable and/or insitu crosslinkable elastomers, using established acrylate chemistry. Forinstance, 5 grams of PXS 1:1 or 1:2 were dissolved in N,N-dimethylformaldehyde (DMF) under anhydrous conditions. 50 mL anhydrous DMF wasadded to a flame dried round-bottom flask to make a 10% solution (w/v)of polymer. After adding 20 mg of DMAP, the reaction flask was placed inan ice bed over a stirring plate under nitrogen. Once cooled, “x” mol ofacryloyl chloride [the value of “x” mol varies for any desired degree ofacrylation which influences biodegradation and mechanical properties ofthe eventual polymer] and equimolar triethylamine was added to start thereaction. The ice-bath was allowed to heat to room temperatureovernight. This solution was filtered, and the acrylated PXS polymers(PXSa 1:1 or PXSa 1:2) were precipitated in a 50/50 ethyl acetate/hexanesolution. The precipitate was allowed to settle at −20° C. overnight andthe solvents were decanted. The PXSa polymers were thoroughly mixed with0.1 weight % UV photoinitiator 2,2-dimethoxy-2-phenyl-acetophenone andphotopolymerized with the addition of ˜4 mW/cm² ultraviolet light for 10minutes using a longwave ultraviolet lamp (model 100AP, Blak-Ray).

Experiment 3.

During its residence in vivo, PXS 1:2 polymers remain completelytransparent, whereas PXS 1:1, PXG 1:1, poly(diol-citrate) (PDC), andpoly(glycerol-sebacate) (PGS) polymers became opaque.

Experiment 4.

During its residence in vivo, PXS 1:2 polymers exhibited little to nodegradation at week 12.

Experiment 5.

Characteristics of PXS polymers. Increasing the sebacic acid to thepolyol by 2-fold (xylitol:sebacic acid=1:2) has a dramatic influence onthe crosslink density (or, Mc as a measure thereof, changes by 10-fold)and contact angle, which renders the elastomer PXS 1:2 with a muchslower degradation profile than PXS 1:1. By increasing the crosslinkdensity by adding more polycarboxylic acids, the crosslink density canbe increased to a number which is not possible by merely changing thecuring conditions of a PXS 1:1 polymer. This increase in crosslinkdensity does not result in a brittle polymer. The strain till failurethat can be put on this polymer (PXS 1:2) is still around 50%elongation, which is much more deformation it can recover from thanother important polymers like collagen (which elongates to maximally 20%(Fratzl et al., J. Struct. Biol. 1998, 122, 119-22; Wang et al., Theor.Appl. Fract. Mech. 1997, 27, 1-12)), or poly(lactide), poly(glycolide),and their co-polymers, which only elongate a few percents. These aboveproperties (degradation profile and mechanical properties) may be due tothe fact that, since the hydroxyl: carboxyl groups are not 1:1 when theamount of the polycarboxylic acid is increased, it allows any freehydroxyls to participate in (extra) hydrogen bonding within the polymerbackbone which might be responsible for the elastic properties.

Experiment 6.

Scanning Electrode Microscopy (SEM). SEM images were taken from the invivo implants that were explanted at predetermined timepoints. As thepolymer PXS 1:1 showed a clear erosion front from the outside towardsthe middle of the polymer network, one can argue that PXS 1:1 acts likea surface degrading polymer rather than a bulk-eroding polymer. Thus,mechanical properties will be more likely to be maintained in vivoduring degradation.

PXS 1:2, however, did not show any disruption of its surface integrity(PXS shows no degradation after 12 weeks in vivo). Degradability can beprecisely controlled by introducing more polycarboxylic acids whichincrease crosslink density and hydrophobicity.

Observed cell attachment and subsequent growth into monolayer for PXS1:1.

Example 2 Biodegradable Xylitol-Based Polymers

In this Example, we describe xylitol-based polymers. Polycondensation ofxylitol with water soluble citric acid yielded biodegradable, watersoluble polymers. Acrylation of this polymer resulted in an elastomericphotocrosslinkable hydrogel. Polycondensation of xylitol with the waterinsoluble sebacic acid monomer produced tough biodegradable elastomers,with tunable mechanical and degradation properties. These xylitol-basedpolymers exhibited excellent in vitro and in vivo biocompatibilitycompared to the well-characterized poly(L-lactic-co-glycolic acid)(PLGA), and are promising biomaterials.

Sebacic acid (a metabolite in the oxidation of fatty acids) and citricacid (a metabolite in the Krebs cycle) were chosen as the reactingmonomers for their proven biocompatibility (Y. Wang, G. A. Ameer, B. J.Sheppard, R. Langer, A tough biodegradable elastomer. Nat Biotechnol2002, 20, (6), 602-606; J. Yang, A. R. Webb, G. A. Ameer, Novel CitricAcid-Based Biodegradable Elastomers for Tissue Engineering. Adv Mater2004, 16, (6), 511-516; each of which is incorporated herein byreference) and they are FDA approved compounds as well. Polycondensationof xylitol with sebacic acid produced water insoluble waxy pre-polymers(designated PXS pre-polymer). PXS pre-polymers with a monomer ratio ofxylitol:sebacic acid of 1:1 and 1:2 were synthesized and had a weightaverage molecular weights (M_(w)) of 2,443 g/mol (M_(n)=1,268 g/mol, PDI1.9) and 6,202 g/mol (M_(n)=2,255 g/mol, PDI 2.7), respectively. The PXSpre-polymers were melted into the desired form and cured bypolycondensation (120° C., 40 mTorr for 4 days) to yield low modulus(PXS 1:1)—and high modulus (PXS 1:2) elastomers. PXS pre-polymers aresoluble in ethanol, dimethyl sulfoxide, tetrahydrofuran and acetone,which allows for processing into more complex geometries.Polycondensation of xylitol with citric acid resulted in a water solublepre-polymer (designated PXC pre-polymer), of which the M_(w) was 298,066g/mol and the M_(n) was 22,305 g/mol (PDI 13.4), compared to linearpoly(ethylene glycol) (PEG) standards. To cross-link the water solublePXC pre-polymer in an aqueous environment, we functionalized thehydroxyl groups of PXC with vinyl groups (designated PXCma) usingmethacrylic anhydride, as previously described for photo-crosslinkablehyaluronic acid (J. A. Burdick, C. Chung, X. Jia, M. A. Randolph, R.Langer, Controlled Degradation and Mechanical Behavior ofPhotopolymerized Hyaluronic Acid Networks. Biomacromolecules 2005, 6,386-391; K. A. Smeds, A. Pfister-Serres, D. Miki, K. Dastgheib, M.Inoue, D. L. Hatchell, M. W. Grinstaff, Photocrosslinkablepolysaccharides for in situ hydrogel formation. J Biomed Mater Res 2001,54, (1), 115-121; each of which is incorporated herein by reference).During this reaction, the M_(w) and M_(n) of the polymer did not changeappreciably. The PXCma pre-polymer was photopolymerized in a 10% w/vaqueous solution using a photoinitiator. This is referred to as thePXCma hydrogel. The synthetic route of these polymers is summarized inFIG. 1.

Fourier-Transformed Infrared Spectroscopy (FT-IR) confirmed ester bondformation in all polymers (FIG. 2A), with a stretch at 1,740 cm⁻¹ whichcorresponds to ester linkages. A broad stretch was also observed atapproximately 3,448 cm⁻¹ which corresponds to hydrogen bonded hydroxylgroups. The FT-IR of PXCma illustrated an additional stretch at 1,630cm⁻¹ compared to the spectrum of PXC, which is associated with thevibration of the vinyl groups. ¹H-NMR revealed a polymer composition of1.10:1 xylitol to sebacic acid for PXS 1:1, 1.08:2 xylitol to sebacicacid for PXS 1:2, and 1.02:1 xylitol to citric acid for PXC. The degreeof substitution of xylitol monomers with a methacrylate group was foundto be 44% for the PXCma pre-polymer (average percentage of xylitolmonomers modified with a methacrylate group).

Ideally, the mechanical properties of an implantable biodegradabledevice should match its implantation site to minimize mechanicalirritation to surrounding tissues and should permit large deformations(Y. Wang, G. A. Ameer, B. J. Sheppard, R. Langer, A tough biodegradableelastomer. Nat Biotechnol 2002, 20, (6), 602-606; incorporated herein byreference), inherent to the dynamic in vivo environment. Allxylitol-based polymers revealed elastic properties (FIG. 2B,C). The PXS1:1 elastomer had an average Young's modulus of 0.82±0.15 MPa with anaverage elongation at failure of 205.2±55.8% and an ultimate tensilestress of 0.61±0.19 MPa. Increasing the crosslink density by doublingthe sebacic acid monomer feed ratio resulted in a stiffer elastomer. ThePXS 1:2 elastomer revealed a Young's modulus of 5.33±0.40 MPa, had anaverage elongation at failure of 33.1±4.9% and an ultimate tensilestress of 1.43±0.15 MPa. The stress versus strain curves of PXS 1:1 andPXS 1:2 are typical for low and high modulus elastomers (FIG. 2B) (Y.Wang, G. A. Ameer, B. J. Sheppard, R. Langer, A tough biodegradableelastomer. Nat Biotechnol 2002, 20, (6), 602-606; incorporated herein byreference). DSC showed a glass transition temperature of 7.3 and 22.9°C. for PXS 1:1 and 1:2 respectively, indicating that these elastomersare in a rubbery state at room- and physiological temperature. Themechanical properties of PXS 1:1 elastomer is similar to a previouslydeveloped elastomer, composed of glycerol and sebacic acid (Y. Wang, G.A. Ameer, B. J. Sheppard, R. Langer, A tough biodegradable elastomer.Nat Biotechnol 2002, 20, (6), 602-606), but showed a higher Young'smodulus for a comparable elongation. Altering monomer feed ratios ofsebacic acid in PXS elastomers resulted in a wide range of crosslinkdensities, whilst maintaining elastomeric properties. The molecularweight between crosslinks (M) ranged in the order of a magnitude (from10517.4±102 g/mol for PXS 1:1 to 1585.1±43 g/mol for PXS 1:2, Table 1)and decreased as more crosslink entities were introduced. Such anappreciable range can otherwise not be obtained by changing condensationparameters of PXS 1:1. The increased crosslink density in PXS 1:2 alsoresulted in significantly less equilibrium hydration as determined bymass differential of PXS 1:2 in ddH₂O (24 hrs at 37° C.), compared toPXS 1:1 (4.1±0.3% and 12.6±0.4% respectively), as well as a lower solcontent (i.e., fraction of free, unreacted macromers within theelastomeric construct, Table 1). In concert with this finding, addingmore sebacic acid molecules within the polymer affects the water-in-aircontact angles (PXS 1:1 26.5±3.6°, PXS 1:2 52.7±5.7°, after 5 minutes),as more aliphatic monomers are being introduced.

TABLE 1 Physical properties of xylitol-based polymers (PXS 1:1 and 1:2are elastomers, PXCma is a photocured hydrogel). M_(c): the molecularweight between crosslinks, calculated with Eqn. 1 for the PXSelastomers, and Eqn. 2 and 3 for the PXCma hydrogel (See Experimental).Young's/ Elongation/ Equilibrium Compression Compression hydration bySol Contact Polymer Crosslink Modulus at break mass Content AngleDensity Density M_(c) Polymer (kPa) (%) (%) (%) (°) (g/cm³) (mol/m³)(g/mol) PXS 1:1 820 ± 150 205.2 ± 55.8 12.6 ± 0.4 11.0 ± 2.7  26.5 ± 3.61.18 ± 0.02 112.2 ± 30.5 10,517.4 ± 102.1 PXS 1:2 5,330 ± 400   33.1 ±4.9  4.1 ± 0.3 1.2 ± 0.8 52.7 ± 5.7 1.16 ± 0.02 729.32 ± 57.3  1,585.1 ±43.7 PXCma 5.8 ± 1.2 79.9 ± 5.6 23.9 ± 6.2 31.7 ± 10.6 n/a 1.51 ± 0.05136.4 ± 27.9 11,072.1 ± 115.8

The equilibrium hydration of PXCma hydrogels determined by mass was23.9±6.2% after 24 hrs at 37° C. Volumetric swelling analysis revealedthat the polymer volume fraction in the relaxed state (ν_(r)), which isimmediately after crosslinking, but before equilibrium swelling, was6.9±0.1% and decreased to 5.8±0.2% at equilibrium swelling, designatedthe polymer volume fraction in the swollen state (ν_(s)). Cycliccompression up to 75% strain of the PXCma hydrogel was possible withoutpermanent deformation, and only limited hysteresis was observed duringcyclic conditioning, revealing the elastic properties over a wide rangeof strain conditions. The PXCma hydrogel failed at a compressive strainof 79.9±5.6% and showed a compressive modulus of 5.84±1.15 kPa (FIG.2C). The mechanical properties of PXCma hydrogel discs were similar tophotocured hyaluronic acid hydrogels (50 kDa 2-5% w/v), as previouslyreported (J. A. Burdick, C. Chung, X. Jia, M. A. Randolph, R. Langer,Controlled Degradation and Mechanical Behavior of PhotopolymerizedHyaluronic Acid Networks. Biomacromolecules 2005, 6, 386-391;incorporated herein by reference), although the PXCma hydrogel showed alower compression modulus for a similar ultimate compression stress. Thephysical properties of the elastomers and the hydrogel are summarized inTable 1.

Xylitol-based biopolymers degrade in vivo. After subcutaneousimplantation, approximately 5% of the mass of the hydrogel was foundafter 10 days. The degradation rate of PXS elastomers varied accordingto the stoichiometric ratios. PXS 1:1 had fully degraded after 7 weeks.However, after 28 weeks, 76.7±3.7% still remained of the PXS 1:2elastomer (FIG. 2D). This demonstrates that the in vivo degradationkinetics of xylitol-based elastomers can be tuned in addition tocrosslink density, surface energy, and equilibrium hydration. Thus, thispolymer platform describes a range in physical properties, which allowfor a tuneable in vivo degradation rate. The PXS 1:2 elastomers wereoptically transparent during the first 15 weeks in vivo and turnedopaque upon degradation (seen at week 28).

Xylitol-based polymers are biocompatible in vitro and in vivo, comparedto the prevalent synthetic polymer PLGA (65/35 LA/GA, high M_(w)).Regardless of the eventual in vivo application of these xylitol basedpolymers, a normal wound healing process upon implantation is mandatory,and is orchestrated by residential fibroblasts. We therefore choseprimary human foreskin fibroblasts (HFF) to test in vitrobiocompatibility. All xylitol-based elastomers and hydrogels weretransparent polymers, which facilitated characterization ofcell-biomaterial interactions. HFFs attached readily to PXS elastomersand proliferated into a confluent monolayer in 6 days. HFFs cultured onPXS elastomers showed a similar cell morphology and proliferation ratecompared to HFFs grown on PLGA (FIG. 3A,B). There was no cell attachmenton PXCma hydrogels. It is known that cells in general do not attach tohydrogels, unless attachment promoting entities are incorporated (D. L.Hem, J. A. Hubbell, Incorporation of adhesion peptides into nonadhesivehydrogels useful for tissue resurfacing. J Biomed Mater Res 1998, 39,266-276; incorporated herein by reference). We therefore examined thecytotoxicity of soluble PXCma pre-polymer in the culture media. HFFsexposed for 4 or 24 hrs to PXCma pre-polymer fractions in the growthmedia (0.01%-1% w/v) were not compromised in their mitochondrialmetabolism, as tested by the MTT assay, compared to HFFs with no PXCmain the growth media (FIG. 3C). Upon subcutaneous implantation, none ofthe animals showed an abnormal post-operative healing process, asassessed clinically and by histology. The PXS 1:1 and 1:2 discs wereencased in a translucent tissue capsule after 1 week, which did notbecome more substantial throughout the rest of the study. Histologicalsections confirmed that the polymer-tissue interface was characterizedby a mild fibrous capsule formation (FIG. 3D ii and iii). No abundantinflammation in the surrounding tissues was seen, and the sectionsshowed a quiet polymer-tissue interface, which is characteristic for thePXS elastomers after the first week in vivo. Also, no perivascularinfiltration was noted in the surrounding tissues of the PXS discs. Thisquiescent tissue response was evident when compared to the tissues incontact with the PLGA implants (FIG. 3Di). Surrounding the PLGAimplants, a more substantial vascularized fibrous capsule was seen, withminor perivascular infiltration (arrow). A comparable thickness offibrous capsule formation was noted for the 10% PXCma hydrogel at day 10(FIG. 3Div). No PXCma hydrogel was found at 14 days after repetitivesectioning of the explanted tissue. Long term histological sections ofPXS 1:1 and 1:2 at week 5 and 12 respectively (FIG. 3Dv and vi),demonstrated that even upon degradation the fibrous capsule remainedquiescent: At week 5 the PXS 1:1 elastomer had degraded approximately73%, whereas the PXS 1:2 polymer showed no degradation at all at week12. Thus, xylitol-based polymers exhibited excellent biocompatibility ascompared to PLGA.

Our goal was to develop a polymer synthesis scheme that requires verysimple adjustments in chemical composition to achieve a wide range inmaterial properties. We have described a process for the synthesis ofxylitol-based polymers. Xylitol is well studied in terms ofbiocompatibility and pharmacokinetics in humans (L. Sestoft, Anevaluation of biochemical aspects of intravenous fructose, sorbitol andxylitol administration in man. Acta Anaesthesiol Scand Suppl 1985, 82,19-29; H. Talke, K. P. Maier, [Glucose, fructose, sorbitol and xylitolmetabolism in man]. Infusionstherapie 1973, 1, (1), 49-56; each of whichis incorporated herein by reference). It is a metabolic intermediate inmammalian carbohydrate metabolism with a daily endogenous production of5-15 g in the adult human (E. Winkelhausen, S. Kuzmanova, MicrobialConversion of D-Xylose to Xylitol. J Ferment Bioeng 1998, 86, (1), 1-14;incorporated herein by reference). The entry into metabolic pathways isslow and independent of insulin, and does not cause rapid fluctuationsof blood glucose levels (S. S, Natah, K. R. Hussien, J. A. Tuominen, V.A. Koivisto, Metabolic response to lactitol and xylitol in healthy men.Am. J. Clin. Nutr. 1997, 65, (4), 947-950; incorporated herein byreference). As a monomer, xylitol is an important compound in the foodindustry where it has an established history as a sweetener with provenanti-cariogenic activity (E. Honkala, S. Honkala, M. Shyama, S. A.Al-Mutawa, Field trial on caries prevention with xylitol candies amongdisabled school students. Caries Res 2006, 40, (6), 508-513;incorporated herein by reference). Moreover, it has an anti-microbialeffect on upper airway infections caused by Gram positive streptococci(M. Uhari, T. Kontiokari, M. Koskela, M. Niemelä, Xylitol chewing gum inprevention of acute otitis media: double blind randomised trial. BMJ1996, 313, (7066), 1180-1184; M. Uhari, T. Tapiainen, T. Kontiokari,Xylitol in preventing acute otitis media. Vaccine 2000, 19, (Suppl 1),S144-147; L. Durairaj, J. Launspach, J. L. Watt, Z. Mohamad, J. Kline,J. Zabner, Safety assessment of inhaled xylitol in subjects with cysticfibrosis. J Cyst Fibros 2007, 6, (1), 31-34; J. Zabner, M. P. Seiler, J.L. Launspach, P. H. Karp, W. R. Kearney, D. C. Look, J. J. Smith, M. J.Welsh, The osmolyte xylitol reduces the salt concentration of airwaysurface liquid and may enhance bacterial killing. Proc Natl Acad Sci USA. 2000, 97, (21), 1161-11619; each of which is incorporated herein byreference). Although xylitol has been studied in polymer synthesis,others have utilized it typically as an initiator (Q. Hao, L. F., Q. Li,Y. Li, L. Jia, J. Yang, Q. Fang, A. Cao, Preparation and crystallizationkinetics of new structurally well-defined star-shaped biodegradablepoly(L-lactide)s initiated with diverse natural sugar alcohols.Biomacromolecules 2005, 6, (4), 2236-2247; incorporated herein byreference), or altered xylitol to yield linear polymers by protectingthree of the five functional groups (M. Gracia Garcia-Martin, E. BenitoHernandez, R. Ruiz Perez, A. Alla, S. Munoz-Guerra, J. A. Galbis,Synthesis and Characterization of Linear Polyamides Derived fromL-Arabinitol and Xylitol. Macromolecules 2004, 37, 5550-5556;incorporated herein by reference). Xylitol-based polymers exposefunctional groups available for functionalization as shown here. Theywere produced in sub-kilogram quantities without the use of organicsolvents or cytotoxic additives. Xylitol-based polymers areendotoxin-free and do not impose a potential immunological threat likebiological polymers extracted from tissues or produced by bacterialfermentation, such as collagen and hyaluronic acid (L. R. Ellingsworth,F. DeLustro, J. E. Brennan, S. Sawamura, J. McPherson, The human immuneresponse to reconstituted bovine collagen. J Immunol 1986, 136, (3),877-882; J. R. Lupton, T. S. Alster, Cutaneous hypersensitivity reactionto injectable hyaluronic acid gel. Dermatol Surg 2000, 26, (2), 135-137;each of which is incorporated herein by reference). In addition, themechanical properties of xylitol-based elastomers fall close to, or arewithin biological values of several tissues, such as acellularperipheral nerve (G. H. Borschel, K. F. Kia, W. M. Kuzon Jr., R. G.Dennis, Mechanical Properties of Acellular Peripheral Nerve. J Surg Res2003, 114, 133-139; incorporated herein by reference), small diameterarteries (V. Clerin, J. W. Nichol, M. Petko, R. J. Myung, W. Gaynor, K.J. Gooch, Tissue Engineering of Arteries by Directed Remodeling ofIntact Arterial Segments. Tissue Eng 2003, 9, (3), 461-472; incorporatedherein by reference), cornea (J. O. Hjortdal, Regional ElasticPerformance of the Human Cornea. J Biomech 1996, 29, (7), 931-942;incorporated herein by reference), and intervertebral discs (D. M.Skrzypiec, P. Pollintine, A. Przybyla, P. Dolan, M. A. Adams, TheInternal Mechanical Properties of Cervical Intervertebral Discs asRevealed by Stress Profilometry. Eur Spine J 2007, 16, (10), 1701-1709;incorporated herein by reference). In this Example, we show threeexamples of possible polymers based on this monomer. Potentialcombinations in chemical composition of xylitol-based polymers arenumerous and therefore it provides a platform to tune mechanicalproperties, degradation profile, and cell attachment.

Experimental

Synthesis and Characterization of the Polymers.

All chemicals were purchased from Sigma-Aldrich unless stated otherwise.Appropriate molar amounts of the polyol and reacting acid monomer weremelted in a round bottom flask at 150° C. under a blanket of inert gas,and stirred for 2 hrs. Vacuum (˜50 mTorr) was applied yielding thepre-polymers PXS 1:1 (12 hrs), PXS 1:2 (6 hrs) and PXC (1 hr). The PXCpolymer was dissolved in ddH₂O and lyophilized. Methacrylated PXCpre-polymer (PXCma) was synthesized by the addition of methacrylicanhydride in a ˜20-fold molar excess as previously described for themethacrylation of hyaluronic acid (K. A. Smeds, A. Pfister-Serres, D.Miki, K. Dastgheib, M. Inoue, D. L. Hatchell, M. W. Grinstaff,Photocrosslinkable polysaccharides for in situ hydrogel formation. JBiomed Mater Res 2001, 54, (1), 115-121; incorporated herein byreference), dialyzed in ddH₂O (M_(w) cutoff 1 kDa) and lyophilized.PXCma hydrogels were fabricated by dissolving 10% w/v PXCma in PBScontaining 0.05% w/v2-methyl-1-(4-(hydroxyethoxy)phenyl)-2-methyl-1-propanone (Irgacure2959, 12959) as the photo-initiator and exposure of ˜4 mW/cm²ultraviolet light (model 100AP, Blak-Ray). All PXS 1:1 and 1:2elastomers were produced by further polycondensation (120° C., 140 mTorrfor 4 days). The pre-polymers were sized using gel permeationchromatography using THF or filtered ddH₂O on Styragel columns (seriesof HR-4, HR-3, HR-2, and HR-1, Waters, Milford, Mass., USA). FT-IRanalysis was carried out on a Nicolet Magna-IR 550 spectrometer. ¹H-NMRspectra were obtained of the PXS pre-polymers in C₂D₆O, and of the PXCmapre-polymers in D₂O on a Varian Unity-300 NMR spectrometer. The chemicalcomposition of the pre-polymers was determined by calculating the signalintegrals of xylitol, and compared to the signal integrals of sebacicacid or citric acid. The signal intensities showed peaks of —OCH₂(CH(OR))₃CH ₂O— at 3.5-5.5 ppm from xylitol, —CH ₂— at 2.3-3.3 ppm fromcitric acid, and peaks of —COCH ₂CH ₂CH ₂— at 1.3, 1.6 and 2.3 ppm fromsebacic acid. The final degree of substitution after acrylation of thePXC pre-polymer was calculated by the signal integral of the protonsassociated with —C(CH ₃)═CH ₂ at 1.9, 5.7 and 6.1 ppm from themethacrylate groups. Tensile tests were performed on hydrated (ddH₂O at37° C.>24 h) dog-bone shaped polymer strips and conducted on an Instron5542 (according to ASTM standard D412-98a). Compression analysis of thephoto-crosslinked PXCma hydrogels was performed as previously described(K. A. Smeds, A. Pfister-Serres, D. Miki, K. Dastgheib, M. Inoue, D. L.Hatchell, M. W. Grinstaff, Photocrosslinkable polysaccharides for insitu hydrogel formation. J Biomed Mater Res 2001, 54, (1), 115-121;incorporated herein by reference). Differential scanning calorimetry(DSC) was done as previously reported (C. L. E. Nijst, J. P. Bruggeman,J. M. Karp, L. Ferreira, A. Zumbuehl, C. J. Bettinger, R. Langer,Synthesis and Characterization of Photocurable Elastomers fromPoly(glycerol-co-sebacate). Biomacromolecules 2007, 8, (10), 3067-3073;incorporated herein by reference). The mass density was measured using apycnometer (Humboldt, MFG. CO). Crosslink density (n) and M_(c) werecalculated from the following equations for an ideal elastomer (P. J.Flory, Principals of Polymer Chemistry. Cornell University Press: NewYork, 1953; incorporated herein by reference):

$\begin{matrix}{n = {\frac{E_{0}}{3{RT}} = \frac{\rho}{M_{c}}}} & {{Eqn}.\mspace{14mu} 1}\end{matrix}$where E₀ is the Young's modulus, R the universal gas constant, Ttemperature and ρ is the mass density. This rubber-elasticity theory canalso be utilized to calculate the effective M_(c) for hydrogels thatreveal elastic behavior and which were prepared in the presence of asolvent, according to Peppas et al. (N. A. Peppas, J. Z. Hilt, A.Khademhosseini, R. Langer, Hydrogels in Biology and Medicine: FromMolecular Principles to Bionanotechnology. Adv Mater 2006, 18,1345-1360; incorporated herein by reference).

$\begin{matrix}{\tau = {\frac{\rho\;{RT}}{M_{c}}\left( {1 - \frac{2M_{c}}{M_{n}}} \right)\left( {a - \frac{1}{a^{2}}} \right)\left( \frac{v_{s}}{v_{r}} \right)^{\frac{1}{3}}}} & {{Eqn}.\mspace{14mu} 2}\end{matrix}$where τ is the compression modulus of the hydrogel, ν_(s) (0.058±0.002)is the polymer volume fraction in the swollen state, and ν_(r)(0.069±0.001) is the polymer volume fraction in the relaxed state. Foran isotropically swollen hydrogel, the elongation ratio (α) is relatedto the swollen polymer volume fraction:α=ν_(s) ^(1/3)  Eqn. 3

The water-in-air contact angle measurements were carried out aspreviously mentioned (Y. Wang, G. A. Ameer, B. J. Sheppard, R. Langer, Atough biodegradable elastomer. Nat Biotechnol 2002, 20, (6), 602-606).Degradation of the explanted polymers was determined by massdifferential, calculated from the polymer's dry weight at t, andcompared to the dry weight at the start of the study. All data wereobtained from at least four samples, and are expressed as means±standarddeviation.

In Vitro and In Vivo Biocompatibility.

Primary human foreskin fibroblasts (HFF, ATCC, Manassas, Va., USA) werecultured in growth media, as previously described (C. L. E. Nijst, J. P.Bruggeman, J. M. Karp, L. Ferreira, A. Zumbuehl, C. J. Bettinger, R.Langer, Synthesis and Characterization of Photocurable Elastomers fromPoly(glycerol-co-sebacate). Biomacromolecules 2007, 8, (10), 3067-3073).Glass Petri dishes (60 mm diameter) contained 3 grams of curedelastomers (120° C., 140 mTorr for 4 days). Petri dishes prepared with a2% w/v PLGA (65/35, high M_(w), Lakeshore Biomedical, Birmingham, Ala.,USA) solution in dichloromethane at 100 uL/cm² and subsequent solventevaporation served as control. Washes with sterile PBS were done beforethe polymer loaded dishes were sterilized by UV radiation. Cells wereseeded (at 2.000 cells/cm²) in the biomaterial-laden dishes, withoutprior incubation of the polymers with growth media. Cells were allowedto grow to confluency and imaged at 4 hrs, and 1, 3, 5 and 6 days afterinitial seeding. Phase micrographs of cells were taken at 10×magnification using Axiovision software (Zeiss, Germany). For cellproliferation measurements, randomly picked areas were imaged and cellswere counted. That cell number was expressed as the percentage increaseof cells compared after initial seeding, designated cell differential.To assess cytotoxicity of the PXCma macromers, cells were seeded intissue culture treated polystyrene dishes at 10.000 cells/cm² andallowed to settle for 4 hrs. After a gentle wash with sterile PBS, 1%,0.5%, 0.1% and 0.01% w/v of PXCma in growth media was added for 4 or 24hrs. Cell viability via mitochondrial metabolism was measured using themethylthiazoletetrazolium (MTT) assay as previously reported (Y. Wang,G. A. Ameer, B. J. Sheppard, R. Langer, A tough biodegradable elastomer.Nat Biotechnol 2002, 20, (6), 602-606). The statistical significancebetween two sets of data was calculated using a two-tailed Student'st-test. For the in vivo biocompatibility and degradation study,elastomeric discs d=10 mm, h=1 mm were implanted. PLGA pellets weremelt-pressed (0.3 g, 172° C., 5000 MPa) into a mold (d=10 mm, h=1 mm)using a Carver Hydraulic Unit Model #3912-ASTM (Carver, Inc. Wabash,Ind.). Female Lewis rats (Charles River Laboratories, Wilmington, Mass.)weighing 200-250 grams were housed in groups of 2 and had access towater and food ad libitum. Animals were cared for according to theprotocols of the Committee on Animal Care of MIT in conformity with theNIH guidelines (NIH publication #85-23, revised 1985). The animals wereanaesthetized using continuous 2% isoflurane/O₂ inhalation. The implantswere introduced by two small midline dorsal incisions, and two polymerformulations (each on one side) were placed in subcutaneous pocketscreated by lateral blunt dissection. The skin was closed with staples.Per time point, three rats were sacrificed, from which four implantswere analyzed for the degradation study, and two implants were resecteden bloc with surrounding tissue and fixed in formalin-free fixative(Accustain). These specimens were embedded in paraffin after a series ofdehydration steps in ethanol and xylene. Sequential sections (8-15 μm)were stained with hematoxilyn and eosine (H&E) and histology wasevaluated by two medical doctors (JPB, DSK). Throughout the study, allrats remained in good general health as assessed by their weight gain.

Example 3 Biodegradable Poly(polyol sebacate) Polymers

In this Example, polyols were reacted with sebacic acid, yielding afamily of thermoset poly(polyol sebacate) (PPS) polymers. Monomers ofPPS polymers have the potential to be metabolized in vivo since sebacicacid is a metabolite in fatty acid oxidation and polyols areintermediates in mammalian carbohydrate metabolism. Polyols such asxylitol, sorbitol, mannitol, and maltitol are biocompatible, FDAapproved, and are metabolized in an insulin-independent manner (K. C.Elwood, Methods available to estimate the energy values of sugaralcohols. Am J Clin Nutr 1995, 62 (Suppl), 1169-1174; S. S, Natah, K. R.Hussien, J. A. Tuominen, V. A. Koivisto, Metabolic response to lactitoland xylitol in healthy men. Am J Clin Nutr 1997, 65, (4), 947-950; L.Sestoft, An evaluation of biochemical aspects of intravenous fructose,sorbitol and xylitol administration in man. Acta Anaesthesiol ScandSuppl 1985, 82, 19-29; each of which is incorporated herein byreference). The functionality and physical properties of the differentpolyols influenced polymer properties. Stoichiometry further allowed fortuning chemical, physical and mechanical properties, as well as in vitroand in vivo degradation rates. PPS polymers show biocompatibilitysimilar to PLGA, and may be promising biomaterials in biomedicalapplications such as reconstructive surgery and tissue engineering.

Materials and Methods

Synthesis and Characterization of PPS Polymers

All chemicals were purchased from Sigma-Aldrich (St. Louis, Mo., USA)unless stated otherwise. Appropriate molar amounts of the polyol andsebacic acid monomer were melted in a 250 mL round bottom flask at 150°C. under a blanket of inert gas, and stirred for 2 h. Vacuum (˜50 mTorr)was applied for 2-12 h, yielding the pre-polymers poly(xylitol sebacate)(PXS) 1:1 and PXS 1:2, poly(sorbitol sebacate) (PSS) 1:1 and PSS 1:2,poly(mannitol sebacate) (PMS) 1:1 and PMS 1:2, and poly(maltitolsebacate) (PMtS) 1:4 (FIG. 4, Table 3-1). The pre-polymers were sizedusing linear polymer standards on gel permeation chromatography (GPC)using tetrahydrofuran (THF) on Styragel columns (series of HR-4, HR-3,HR-2, and HR-1, Waters, Milford, Mass., USA). ¹H-NMR spectra wereobtained of all pre-polymers in (CD₃)₂NCOD, on a Varian Unity-300 NMRspectrometer. The chemical composition of the pre-polymers wasdetermined by comparing the signal integrals of the polyol, and comparedto the signal integrals of sebacic acid. The signal intensities showedpeaks of —OCH ₂(CH(OR))_(n)CH ₂O— at 3.5-5.5 ppm from the polyol, andpeaks of —COCH ₂CH ₂CH ₂— at 1.3, 1.6 and 2.3 ppm from sebacic acid. ThePPS polymers were produced by another polycondensation step using120-150° C. under vacuum (˜2 Pa) for 4 days (see Table 3-2 for specificcuring conditions). Attenuated total reflectance-Fourier transforminfrared spectroscopy (ATR-FTIR) analysis was performed on these polymernetworks using a Nicolet Magna-IR 500 spectrophotometer. The wettabilityof PPS polymers was determined by contact-angle measurements, and thehydration of these polymers, determined by mass differential after 24 hin ddH₂O at 37° C. The water-in-air contact angle of polymer films wasmeasured using the sessile-drop method and VCA2000 image analysissoftware (n=10). Tensile tests were performed on hydrated (ddH₂O at 37°C.>24 h) dog-bone shaped polymer strips (n=4) and conducted on anInstron 5542 (according to ASTM standard D412-98a) using a 50 or a 500 Nload cell equipped with Merlin software. Glass transition temperature(T_(g)) and other potential phase transitions were measured within thetemperature range of −90° C. and 250° C. with a heating/cooling rate of10° C. per minute using a Q1000 DSC equipped with Advantage Softwarev2.5 (TA Instruments, Newcastle, Del. USA) and analyzed with UniversalAnalysis Software v4.3A (TA Instruments). The mass densities weremeasured using a pycnometer (Humboldt, MFG. CO), and crosslink density(n) as well as the relative molecular mass between crosslinks (M_(c))were calculated from the following equations for an ideal elastomer,where E₀ is the Young's modulus, R is the universal gas constant, T isthe temperature and ρ is the mass density:

$\begin{matrix}{n = {\frac{E_{o}}{3{RT}} = \frac{\rho}{M_{c}}}} & {{Eqn}.\mspace{14mu} 1}\end{matrix}$

TABLE 2 Composition T_(m) ^(a) M_(w) M_(n) Pre-polymer by ¹H-NMR (° C.)(g/mol) (g/mol) PDI PXS 1:1 1.10:1.00 ~80 2443 1268 1.9 PXS 1:21.08:2.00 ~100 6202 2255 2.7 PSS 1:1 0.91:1.00 ~80 6093 3987 1.5 PSS 1:20.89:2.00 ~100 23013 8990 2.6 PMS 1:1 0.99:1.00 ~100 3182 2038 1.6 PMS1:2 1.06:2.00 ~120 10097 4379 2.3 PMtS 1:4 1.18:4.00 ~130 13265 2992 4.4^(a)T_(m)s are temperatures where the polymer revealed a transition froma white, opaque wax to a clear flowing liquid.

TABLE 3 Ultimate Polymer Young's Tensile Ultimate Contact (curingModulus Stress Elongation Angle T_(g) Hydration by ρ M_(c) condition)(MPa) (MPa) (%) (°) (° C.) Mass (%) (g/cm³) n (mol/m³) (g/mol) PXS 1:10.82 ± 0.15 0.61 ± 0.19 205.16 ± 55.76 26.5 ± 3.6 7.3 5.10 ± 0.12 1.18 ±0.02 112.2 ± 30.5 10517.4 ± 102.1 (120° C., 2 Pa, 4 d) PXS 1:2 5.33 ±0.40 1.43 ± 0.15 33.12 ± 4.85 52.7 ± 5.7 22.9 1.74 ± 0.1  1.16 ± 0.02729.32 ± 57.3  1585.1 ± 43.7 (120° C., 2 Pa, 4 d) PSS 1:1 0.37 ± 0.080.57 ± 0.15 192.24 ± 60.12  9.6 ± 3.0 18.1 6.28 ± 0.27 1.13 ± 0.04  50.6± 10.3 22320.1 (120° C., 2 Pa, 5 d) PSS 1:2 2.67 ± 0.12 1.16 ± 0.33 65.94 ± 24.87 36.6 ± 3.1 26.9 1.80 ± 0.09 1.16 ± 0.02 365.3 ± 21.53175.2 (120° C., 2 Pa, 4 d) PMS 1:1 2.21 ± 0.21 0.79 ± 0.10 50.54 ± 9.0132.2 ± 9.0 16.5 4.45 ± 0.14 1.18 ± 0.02 302.4 ± 60.2 3902.2 (140° C., 2Pa, 5 d) PMS 1:2 12.82 ± 2.90  3.32 ± 0.76  44.99 ± 11.81 40.4 ± 9.332.2 1.82 ± 0.15 1.16 ± 0.03 1754.2 ± 242.4 661.3 (140° C., 2 Pa, 5 d)PMtS 1:4 378.0 ± 33.0  17.64 ± 1.30  10.90 ± 1.37 26.3 ± 8.4 45.6 1.40 ±0.03 1.18 ± 0.01 n/a n/a (150° C., 2 Pa, 5 d)In Vitro Degradation of PPS Polymers

Degradation rates via hydrolysis were observed of sol-free PPS samples(n=4) continuously agitated at 37° C. in 20 mL PBS containing sodiumazide (0.05% w/v), or in 20 mL of 0.1 M NaOH at 37° C. as previouslyreported (J. Yang, A. R. Webb, S. J. Pickerill, G. Hageman, G. A. Ameer,Synthesis and evaluation of poly(diol citrate) biodegradable elastomers.Biomaterials 2006, 27, (9), 1889-1898; incorporated herein byreference). At designated time points, samples were removed, washed inddH₂O, incubated in ethanol overnight, dried at 90° C. for 1 d andweighed again to determine mass loss. Mass loss was calculated from dryweight at t (M_(t)) and compared to the dry weight at the start of thestudy (M₀) using the following equation:

$\begin{matrix}{M_{Loss} = {\frac{M_{o} - M_{t}}{M_{o}} \times 100\%}} & {{Eqn}.\mspace{14mu} 2}\end{matrix}$In Vitro Biocompatibility of PPS Polymers

Glass Petri dishes (60 mm diameter, Fisher Scientific) contained 3 g ofcured elastomers (120° C., 140 mTorr for 4 days). Petri dishes preparedwith a 1.5% w/v PLGA (65/35, high M_(w), Lakeshore Biomedical,Birmingham, Ala., USA) solution in dichloromethane at 60 uL/cm² andsubsequent solvent evaporation served as control. Washes with sterilePBS were done and before the polymer loaded dishes were autoclaved.Primary human foreskin fibroblasts (HFF, ATCC, Manassas, Va., USA) werecultured in high glucose Dulbecco's Minimal Essential Medium (DMEM)supplemented with 10% (v/v) fetal bovine serum (Invitrogen), 100 μg/mLstreptomycin (Invitrogen), and 100 U/mL penicillin (Invitrogen). Cellsbetween passage three and six were harvested using trypsin 0.025%/EDTA0.01% and quenched with an equal volume of medium to resuspend thecells. Additional cell systems were chosen from tissues with mechanicalproperties that match, or fall close to the mechanical properties ofspecific PPS polymers tested. A human bone cell line derived from anosteosarcoma (OS) (CRL-1545, ATCC, Manassas, Va., USA) was cultured inPMtS 1:4 coated dishes. A human muscle cell line derived from arhabdomyosarcoma (RMS) (CCL-136, ATCC, Manassas, Va., USA) was culturedin PSS 1:1 coated dishes. Bovine articular chondrocytes (BAC) wereharvested from femoropatellar grooves of 2-4 week-old bovine calves, aspreviously described (Tognana et al., Adjacent tissues (cartilage, bone)affect the functional integration of engineered calf cartilage in vitro.Osteoarthritis Cartilage 2005, 13, (2), 129-38; incorporated herein byreference) and cultured in PMS 1:2 coated dishes. Human umbilical veinendothelial cells (HUVECs) (Cambrex, Walkersville, Md.) were cultured onPXS 1:1 laden dishes, in EGM-2 media supplemented with SingleQuot Kits(Cambrex). HUVECs were used by passage five and in accordance with themanufacturer's instructions. The fibroblasts and tissue specific cellswere seeded (at 7500 cells/cm²) in PLGA- or PPS-laden dishes and wereallowed to grow to a confluent cell monolayer at 37° C. and 5% CO₂,whilst imaged after 4 h and every subsequent day after initial seeding.Phase micrographs of cells were taken at 10× magnification usingAxiovision software (Zeiss). For cell proliferation measurements,randomly picked areas were imaged and cells were counted and averaged.The area and circularity (G. Thurston, B. Jaggi, B. Palcic, Measurementof cell motility and morphology with an automated microscope system.Cytometry 1988, 9, (5), 411-417; incorporated herein by reference) ofcell populations were calculated manually using perimeter and areameasurements by using Axiovision software (Zeiss). The circularity C wascalculated using the following formula:

$\begin{matrix}{C = \frac{4\pi\; A}{P^{2}}} & {{Eqn}.\mspace{14mu} 3}\end{matrix}$where A is the projected area of the cell and P is the perimeter of thecell. Circularity was used as an index of cell spreading. Three distinctcell populations (n=˜80 total) were measured to find cell populationmeans.In Vivo Biocompatibility of PPS Polymers

PPS discs (d=10 mm, h=1 mm) were implanted. Comparable PLGA pellets weremelt-pressed (0.3 g, 172° C., 5000 MPa) into a mold (d=10 mm, h=1 mm)using a Carver Hydraulic Unit Model #3912-ASTM (Carver, Inc. Wabash,Ind.). Two female Lewis rats (Charles River Laboratories, Wilmington,Mass.) weighing 200-250 grams had access to water and food ad libitum.Animals were cared for according to the protocols of the Committee onAnimal Care of MIT in conformity with the NIH guidelines (NIHpublication #85-23, revised 1985). The animals were anaesthetized usingcontinuous 2% isoflurane/O₂ inhalation. The implants were introduced bythree small midline dorsal incisions, and five polymer formulations wereplaced in subcutaneous pockets created by blunt lateral dissection. Theskin was closed with staples. Rats were sacrificed, the implants wereresected en bloc with surrounding tissue and fixed in formalin-freefixative (Accustain). These specimens were embedded in paraffin after aseries of dehydration steps in ethanol and xylene. Sequential sections(8-15 μm) were stained with hematoxliyn and eosine (H&E) and histologywas evaluated by a medical doctor (JPB). Throughout the study, all ratsremained in good general health as assessed by their weight gain.

Statistical Analysis

Two-tailed student's t-tests with unequal variances were performed todetermine statistical significance, where appropriate (Microsoft Excel,Redmond, Wash. USA). Non-parametric one-way ANOVA tests were alsoperformed where appropriate (GraphPad Prism 4.02, GraphPad Software, SanDiego, Calif. USA). Dunn's multiple comparison post-tests were used todetermine significance between specific treatments. All tabulated andgraphical data is reported as mean±S.D. Significance levels were setat * p<0.05.

Results

Pre-Polymer Synthesis and Characterization

All pre-polymers were prepared through bulk polycondensation reactionsof polyol and sebacic acid monomers (FIG. 4). The followingstoichiometric ratios were prepared: PXS 1:1 and 1:2, PSS 1:1 and 1:2,PMS 1:1 and 1:2, and PMtS 1:4. FIG. 5A shows a typical ¹H-NMR spectrumof a PPS pre-polymer. The signal intensities showed peaks of —OCH₂(CH(OR))₃CH ₂O— at 3.5-5.5 ppm from the polyol (mannitol in this case),and peaks of —COCH ₂CH ₂CH ₂— at 1.3, 1.6, and 2.3 ppm from sebacicacid. The chemical composition of the pre-polymers was determined bycalculating the ratios of the signal integrals of the polyol to sebacicacid. ¹H-NMR revealed polymer compositions that are summarized in Table2. In addition, weight average molecular weight (M_(w)), number averagemolecular weight (M_(n)) and polydispersity index (PDI) for all PPSpre-polymers were determined by GPC, and are shown in Table 2. Nodistinct, broad peaks associated with a melting temperature (T_(m))could be detected with DSC for the pre-polymers, most likely due to thepolydispersity of the pre-polymers. Empirically, different temperatureswere used to process these pre-polymers, and are listed in Table 2 aswell. All polymers are clear, viscous liquids at 130° C., and waxy,opaque materials at room temperature. The pre-polymers are soluble incommon solvents like ethanol, acetone, dimethyl sulfoxide,tetrahydrofuran, and dimethylformamide.

Characterization and Physical Properties of PPS Polymers

The pre-polymers were thermally cured into thermoset networks underdifferent curing conditions, as summarized in Table 3. FT-IR of thecured polymers confirmed ester bond formation in all polymers, with astretch at 1,740 cm⁻¹ which corresponds to the ester linkages. A broadstretch was also observed at approximately 3,448 cm⁻¹ which correspondsto hydrogen bonded hydroxyl groups. The FT-IR spectrum of PMtS 1:4illustrated an additional stretch at 1,050 cm⁻¹, compared to the spectraof the other PPS polymers, which is associated with the vibration of theether bond within the maltitol monomer (FIG. 5B).

The thermal properties of the PPS polymers were revealed by DSC: PXS1:1, PSS 1:1 and PMS 1:1 had glass-transition temperatures below roomtemperature. PXS 1:2, PSS 1:2, and PMS 1:2 had glass-transitiontemperatures higher than the 1:1 stoichiometries, but still remainedbelow 37° C., indicating that these PPSs are rubbery at physiologicaltemperatures. PMtS 1:4 showed the highest glass transition temperature,at 45° C., demonstrating that this polymer is glassy at 37° C. (Table3).

Increasing the sebacic acid monomer feed ratio resulted in a highercrosslink density and in lesser wettability of the polymers, asdemonstrated by the hydration as well as higher contact anglemeasurements, as summarized in Table 3.

Mechanical Properties of PPS Polymers

All hydrated PPS polymers, with the exception of PMtS 1:4, showed stressversus strain plots that are typical of hydrated high and low modulusPPS elastomers above their T_(g). FIG. 6A, B show representative stressversus strain plots for the PPS polymers studied herein. The averagetensile Young's modulus, ultimate tensile strength (UTS) and elongationat break for all PPS polymers are summarized in Table 3. PMtS 1:4 wasobserved to be the stiffest material and revealed a tensile Young'smodulus of 378±33.0 MPa, UTS of 17.6±1.30 MPa, and average elongation atbreak of 10.90±1.37% (Table 3, FIG. 6A). PSS 1:1 was observed to be thesoftest material with a tensile Young's modulus of 0.37±0.08 MPa, UTS of0.57±0.15 MPa and elongation at break of 192.24±60.12%. Limitedhysteresis was seen after 1000 cyclic compression cycles up to 50 N forthe PXS 1:1 elastomer as shown in FIG. 6C. Also, PPS pre-polymers aremiscible and allowed for formation of co-polymers. As an example, threePXS 1:1 and PMtS 1:4 co-polymers were produced. Representative stressversus strain plots for different PXS 1:1/PMtS 1:4 w/w ratios are shownin FIG. 6D: the tensile Young's moduli of these PXS 1:1/PMtS 1:4co-polymers were 7.25±0.47 MPa, 3.94±0.32 MPa and 1.61±0.22 MPa for the25/75, 50/50 and 75/25 PXS 1:1/PMtS 1:4 w/w ratios respectively.

In Vitro Degradation of PPS Polymers

Biodegradable polyesters can degrade through hydrolysis. Therefore, thein vitro degradation under physiological conditions was investigated.Mass loss was detected for all PPS polymers (FIG. 7A). After 105 days,PXS 1:1 and 1:2 revealed a mass loss of a mere 1.78±0.30% and 1.88±0.22%respectively. PXS 1:1 did not reveal a similar mass loss profile as PSS1:1 (15.66±1.75%) and PMS 1:1 (21.90±6.99%): the latter two polymers haddegraded more than their corresponding 1:2 stoichiometries (PSS 1:2(5.57±1.00%) and PMS 1:2 (9.00±0.54%)). At this point, PMtS 1:4 showedthe least mass loss of 0.76±0.30% (FIG. 7A). Although degradation underphysiological conditions was observed for all PPS polymers, anadditional in vitro degradation study in high pH (0.1 N NaOH) wasperformed as previously described (J. Yang, A. R. Webb, S. J. Pickerill,G. Hageman, G. A. Ameer, Synthesis and evaluation of poly(diol citrate)biodegradable elastomers. Biomaterials 2006, 27, (9), 1889-1898). Again,all polymers revealed a mass loss over a course of 50 h, and showedresemblance to what was found in the previous degradation study: at 50h, PMtS 1:4 revealed a mass loss of 4.07±2.80%, and PXS 1:1 and 1:2 amass loss of 4.40±0.33% and 4.24±0.52% respectively. PSS 1:1 and PMS 1:1had fully degraded under 20 h. Also in concert with the previousdegradation study, PSS 1:2 and PMS 1:2 degraded slower than the 1:1stoichiometric ratios. After 50 h, 74.10±0.41% of the original mass ofPSS 1:2, and 13-7.45% of PMS 1:2 remained (FIG. 7B).

In Vitro Biocompatibility

The biocompatibility of PXS 1:1 and PXS 1:2 elastomers has been reportedelsewhere (J. P. Bruggeman, C. J. Bettinger, C. L. E. Nijst, D. S.Kohane, R. Langer, Biodegradable Xylitol-Based Polymers. Adv Mater.2008, accepted; J. P. Bruggeman, C. J. Bettinger, R. Langer, ThermosetBiodegradable Xylitol-Based Elastomers: Degradation Profile andBiocompatibility. Submitted 2008; each of which is incorporated hereinby reference). We therefore conducted an initial in vitrobiocompatibility of the other PPS polymers with primary HFFs, asfibroblasts are important regulators of the wound-healing process invivo. The initial attachment and subsequent proliferation into aconfluent cell monolayer was compared to PLGA (FIG. 8). HFFs readilyattached on all but PSS 1:1 and PMS 1:1 polymers. A confluent cell layerwas achieved after 5 d for all substrates, except PSS 1:2 (achieved at 7d, data not shown). Sporadic attachment was seen on PSS 1:1 and PMS 1:1substrates (FIG. 8A, B, D). The cells that attached to PSS 1:1 and PMS1:1 did not spread and did not subsequently proliferate into a confluentmonolayer.

In Vivo Biocompatibility and Degradation

The in vivo biocompatibility of PPS polymers was evaluated viasubcutaneous implantation in rats. After 10 days in vivo, the acuteinflammatory response was mild for all implanted polymers. Thesurrounding tissues did not show necrosis, nor an abundant perivascularinfiltration of mononuclear cells. In addition, the fibrous capsulessurrounding the PPS polymers were thin (FIG. 9A-E). The assessment ofthe chronic inflammatory response after 12 weeks to the implants (FIG.10), revealed thicker fibrous capsules in comparison to the acuteinflammatory response at 10 days. The fibrous capsule formationsurrounding PPS polymers however, seemed similar, or less to theprevalently used PLGA at 12 weeks (FIG. 10E). At this point, the chronicinflammation was still mild, as suggested by the thicknesses of thesecapsules and the presence of few visible vessels within the capsules(FIG. 10A-D). The PSS 1:1 elastomer appeared to have fully degraded atthis time, without detectable traces, despite repetitive sectioning ofthe implantation area.

Initial In Vitro Biocompatibility Analysis of PPS for Tissue SpecificApplications

In vitro attachment and subsequent proliferation into a confluent cellmonolayer of tissue specific cell lines and primary cells were assessedby light microscopy (FIG. 11). PMtS 1:4 revealed similar attachment andgrowth rate of a human osteosarcoma (OS) cell line (derived from bone)compared to PLGA. In addition, cell morphology, as assessed bycircularity and cell area, was not significantly different for OS cellsthat were cultured on PLGA (FIG. 11A i-v). A difference in cellmorphology was found however, for a rhabdomyosarcoma (RMS) cell line(human muscle origin) that was cultured on PSS 1:2 substrates, andcompared to PLGA (FIG. 11B i). RMS cells revealed more spindle likemorphology before a confluent cell layer was achieved, as shown in FIG.11B ii-v: cell circularity was significantly less for cells cultured onPSS 1:2 (p<0.05). In addition, RMS cells spread more, resulting in alarger cell area (p<0.05) (FIG. 11B iii). Initial attachment andsubsequent cell numbers during proliferation were not different fromPLGA. Cell numbers however, did reveal a significant difference forprimary bovine articular chondrocytes (BAC) after 4 and 6 d culture onPMS 1:2, compared to PLGA (FIG. 11C i). A difference in chondrocytemorphology was also noted. Although cell area was greater for BACscultured on PMS 1:2 (p<0.05), cell circularity was not significantlydifferent (p>0.05) (FIG. 11C ii-v). HUVECs were cultured on PXS 1:1 andexhibited attachment, growth rates and cell morphology that werecomparable to PLGA (FIG. 11D i-v).

Discussion

The synthesis of PPS polymers is straightforward and does not requirethe use of organic solvents or cytotoxic additives. The PPS polymerswere produced in sub-kilogram quantities and are inexpensive. The firstpolycondensation step yields PPS pre-polymers that allowed processinginto various scaffold geometries, after which the secondpolycondensation step cures the pre-polymers into a set crosslinkedpolymer network of desired shape. The curing conditions can be adjustedto modify crosslink densities of these networks within a modest range(C. J. Bettinger, J. P. Bruggeman, J. T. Borenstein, R. S. Langer, Aminoalcohol-based degradable poly(ester amide) elastomers. Biomaterials2008, 29, (15), 2315-2325; incorporated herein by reference). However,adjusting stoichiometry allowed for a much wider range of crosslinkdensities and subsequent polymer properties (Table 3). The reactingstoichiometry of sebacic acid to polyol was chosen such that the numberof hydroxyl functionalities of the polyol was always greater than thenumber of carboxylic functionalities by 1 or 2, to ensure step-growthpolymerization and still expose free hydroxyl groups in the polymerbackbone. These free hydroxyl groups may contribute in intra-networkhydrogen bond formation and be available for functionalizationchemistries, such as previously shown (C. L. E. Nijst, J. P. Bruggeman,J. M. Karp, L. Ferreira, A. Zumbuehl, C. J. Bettinger, R. Langer,Synthesis and Characterization of Photocurable Elastomers fromPoly(glycerol-co-sebacate). Biomacromolecules 2007; incorporated hereinby reference).

Of the PPS polymers, PXS and PSS revealed comparable physical andmechanical properties, most likely because their polyol monomers haveT_(m)s close to each other (95 and 97° C. respectively) and have similarwater solubility. PSS elastomers showed slightly lower contact anglesand a higher degree of hydration, compared to PXS (Table 3). Usingmannitol as a monomer produced PPS polymer films with higher Young'smoduli and T_(g)s than PSS elastomers (FIG. 6), as well as highercontact angles (Table 3). Mannitol is a stereoisomer of sorbitol with ahigher T, (165° C.) and lower water solubility, which may explain thedifferences observed between PSS and PMS elastomers. Maltitol-basedpolymers on the other hand, showed similar contact angles as PXS and PSS1:2 stoichiometries, which can be explained if PMtS 1:4 is essentiallyviewed as a glucose:sorbitol:sebacate 1:1:4 polymer. However, maltitolallowed for higher sebacic acid monomer feed ratios, resulting in a highdegree of crosslinking, and therefore in a glassy polymer with a T_(g)above ambient and physiological temperatures, and of which water-uptakeis limited (FIG. 6, Table 3). The tensile Young's moduli of PMtS 1:4polymers are comparable to trabecular bone (50-100 MPa) and maypotentially be developed for bone tissue engineering or osteosynthesismaterials (K. S. Anseth, V. R. Shastri, R. Langer, Photopolymerizabledegradable polyanhydrides with osteocompatibility. Nat Biotechnol 1999,17, 156-159; incorporated herein by reference). Thus, this polymerdesign presents elastomers with Young's moduli that ranged from softelastomeric materials (˜0.4 MPa) in a rubbery state, to elastomers withhigh moduli (˜380 MPa) that are glassy at physiological temperatures. Inaddition, co-polymers of PPS polymers can be produced as well.

The in vivo degradation mechanism PXS elastomers is dominated by surfaceerosion, as reported elsewhere. It is postulated that a higher crosslinkdensity as well as the introduction of more hydrophobic entities(sebacic acid) were responsible for tuning the in vivo degradation rate.In vitro hydrolysis under physiological conditions occurred for all PPSpolymers and revealed similar differences between the 1:1 and 1:2stoichiometries, as was observed in vivo for PXS. However, in vitrodegradation of PXS elastomers was significantly less than PSS and PMSelastomers, and comparable to the PMtS 1:4 polymer under similarconditions (FIG. 7A). This hydrolysis profile was confirmed forhydrolysis in a high pH environment (FIG. 7B). In vitro degradationrates of PXS however, did clearly not correspond to in vivo degradationrates. Similarly, during the in vivo biocompatibility study presentedhere, we observed that the PSS 1:1 polymer appeared to completelydegrade within 12 weeks, but had only lost 15.66±1.75% of its originalmass after 105 days in vitro. This in vivo mass loss of PSS 1:1 issimilar to the previously observed degradation of PXS 1:1, which had anin vivo half life of 3-4 weeks.

PPS polymers support cell attachment with the exception of PSS 1:1 andPMS 1:1 elastomers (FIG. 8). The in vitro cell attachment andproliferation studies were performed without pre-treating or coating thepolymers with adhesion proteins such as fibronectin and collagen. Ifcellular attachment is not warranted, which can be important in someapplications (D. Motlagh, J. Yang, K. Y. Lui, A. R. Webb, G. A. Ameer,Hemocompatibility evaluation of poly(glycerol-sebacate) in vitro forvascular tissue engineering. Biomaterials 2006, 27, (24), 4315-4324; K.E. Schmalenberg, K. E. Uhrich, Micropatterned polymer substrates controlalignment of proliferating Schwann cells to direct neuronalregeneration. Biomaterials 2005, 26, (12), 1423-1430; each of which isincorporated herein by reference), PSS 1:1 and PMS 1:1 can potentiallybe used as a (patterned) coatings, including contact guidance cues ontothe biomaterial (D. M. Thompson, H. M. Buettner, Neurite outgrowth isdirected by schwann cell alignment in the absence of other guidancecues. Ann Biomed Eng. 2006, 34, (1), 161-168; incorporated herein byreference). Alternatively, PSS 1:1 and PMS 1:1 elastomers could bemodified with adhesion-promoting proteins and peptides by grafting themonto the exposed hydroxyl groups.

The fibrous capsules during the acute inflammatory response to PPSforeign materials seemed consistent with fibrous capsule thicknesses ofpreviously reported values for soft thermoset elastomers (FIG. 9) (Y.Wang, G. A. Ameer, B. J. Sheppard, R. Langer, A tough biodegradableelastomer. Nat Biotechnol 2002, 20, (6), 602-606; J. P. Bruggeman, C. L.E. Nijst, C. J. Bettinger, J. M. Karp, M. Moore, R. Langer, D. S.Kohane, In vivo behavior of Poly(glycerol-co-sebacate)-acrylate:implications for a nerve guide material. Submitted 2008; J. P.Bruggeman, C. J. Bettinger, C. L. E. Nijst, D. S. Kohane, R. Langer,Biodegradable Xylitol-Based Polymers. Adv Mater. 2008, Accepted; J.Yang, A. R. Webb, S. J. Pickerill, G. Hageman, G. A. Ameer, Synthesisand evaluation of poly(diol citrate) biodegradable elastomers.Biomaterials 2006, 27, (9), 1889-1898; J. P. Bruggeman, C. J. Bettinger,R. Langer, Thermoset Biodegradable Xylitol-Based Elastomers: DegradationProfile and Biocompatibility. Submitted 2008; C. J. Bettinger, J. P.Bruggeman, J. T. Borenstein, R. S. Langer, Amino alcohol-baseddegradable poly(ester amide) elastomers. Biomaterials 2008, 29, (15),2315-2325; each of which is incorporated herein by reference). However,the fibrous capsules of the chronic inflammatory response surroundingthe higher modulus materials (PMS 1:2 and PMtS 1:4), seemed morepronounced than observed for PSS 1:2 and PMS 1:1, but was still lessthan reported values for PLA and PLGA polymers, which are frequentlyreported around 400-600 microns thick (FIG. 10) (Y. Wang, G. A. Ameer,B. J. Sheppard, R. Langer, A tough biodegradable elastomer. NatBiotechnol 2002, 20, (6), 602-606; Y. Wang, Y. M. Kim, R. Langer, Invivo degradation characteristics of poly(glycerol sebacate). J BiomedMater Res A 2003, 66, (1), 192-7; P. Mainil-Varlet, S. Gogolewski, P.Nieuwenhuis, Long-term soft tissue reaction to various polylactides andtheir in vivo degradation. J Biomed Mater Res A 1996, 7, (12),6713-6721; each of which is incorporated herein by reference).

Thus, PPS polymers are composed of structural units that are endogenousto the mammalian metabolism, but have advantages associated withsynthetic polymers. PPS polymers revealed mechanical properties that canpotentially be useful in a variety of surgical procedures and tissueengineering applications. As an example, human ulnar metacarpophalangealthumb joint ligament has a tensile stress and a Young's modulus of11.4±1.2 MPa and 37.3±5.1 MPa respectively (K. Firoozbakhsh, I. S. Yi,M. S. Moneim, Y. Umada, A study of ulnar collateral ligament of thethumb metacarpophalangeal joint. Clin Orthop Relat Res. 2002, 403,240-247; incorporated herein by reference), and several human cervicalspinal components such as intervertebral discs, as well as theirassociated ligaments, have mechanical properties (S. K. Ha, Finiteelement modeling of multi-level cervical spinal segments (C₃-C₆) andbiomechanical analysis of an elastomer-type prosthetic disc. Med EngPhys. 2006 July, 28(6), 534-41 2006, 28, (6), 534-541; incorporatedherein by reference) that fall within the limits of the PPS polymerplatform shown here. This is also true for softer tissues such as nerves(B. L. Rydevik, M. K. Kwan, R. R. Myers, R. A. Brown, K. J. Triggs, S.L. Woo, S. R. Garfin, An in vitro mechanical and histological study ofacute stretching on rabbit tibial nerve. J Orthop Res 1990, 8, (5),694-701; incorporated herein by reference) and blood vessels (V. Clerin,J. W. Nichol, M. Petko, R. J. Myung, W. Gaynor, K. J. Gooch, TissueEngineering of Arteries by Directed Remodeling of Intact ArterialSegments. Tissue Eng 2003, 9, (3), 461-472; incorporated herein byreference) for instance. For musculoskeletal tissue engineering andreconstructive surgery purposes, PPS polymers seem promising materials(FIG. 11).

Conclusions

PPS polymers are synthetic in nature but have the advantage of beingcomposed of structural units endogenous to human metabolism. Chemical,physical, and mechanical properties as well as degradation rates of thepolymers described in this Example can be tuned by altering the polyoland stoichiometry of the reacting sebacic acid. Potentially, manyco-polymers and composite materials are possible, resulting in aconsiderable number of polymers accessible through the synthetic schemepresented here. PPS polymers exhibited comparable biocompatibility tomaterials approved for human use, such as PLGA.

Example 4 Biodegradable Xylitol-Based Elastomers Degradation Profile andBiocompatibility

We have recently developed a versatile platform of biodegradableelastomers, based on polycondensation reactions of xylitol with sebacicacid, referred to as poly(xylitol sebacate) (PXS) elastomers (J. P.Bruggeman, C. J. Bettinger, C. L. E. Nijst, D. S. Kohane, R. Langer,Biodegradable Xylitol-Based Polymers. Adv Mater 2008; which isincorporated herein by reference). In this Example, we describe thesynthesis and in vivo behavior of an array of thermoset PXS elastomersin detail. Three PXS elastomer formulations were synthesized by alteringthe stoichiometric ratios of xylitol and sebacic acid. An additionalformulation was produced through a co-polymerization strategy. PXSelastomers were characterized in vivo and exhibited enhancedbiocompatibility compared to PLGA. More importantly, PXS elastomersdisplayed structural integrity and form stability throughoutdegradation. The half-life of these elastomers ranged from ˜3 weeks to˜52 weeks. Based on morphological evaluation of PXS implants, we proposea surface eroding mechanism for PXS elastomers.

Materials and Methods

Synthesis and Characterization of PXS Pre-Polymers

All chemicals were purchased from Sigma-Aldrich (St. Louis, Mo., USA)unless otherwise stated. Appropriate molar amounts of the polyol andreacting acid monomer were melted in a round bottom flask at 150° C.under a blanket of inert gas, and stirred for 2 h. Vacuum (˜50 mTorr)was applied yielding the pre-polymers PXS 1:1 (12 h), PXS 2:3 (6 h) andPXS 1:2 (6 h). The pre-polymers were sized using gel permeationchromatography (GPC) using tetrahydrofuran on Styragel columns (seriesof HR-4, HR-3, HR-2, and HR-1, Waters, Milford, Mass., USA) and linearstandards. FT-IR analysis was carried out on a Nicolet Magna-IR 550spectrometer. ¹H-NMR spectra were obtained of the PXS pre-polymers inC₂D₆O, on a Varian Unity-300 NMR spectrometer. The chemical compositionof the pre-polymers was determined by calculating the signal integralsof xylitol, and compared to the signal integrals of sebacic acid. Thesignal intensities showed peaks of —OCH ₂(CH(OR))₃CH ₂O— at 3.5-5.5 ppmfrom xylitol, and peaks of —COCH ₂CH ₂CH ₂— at 1.3, 1.6 and 2.3 ppm fromsebacic acid.

Synthesis and Characterization of PXS Elastomers

All PXS polymers were produced by further polycondensation (120° C., 140mTorr for 4 days. Tensile tests were performed on dog-bone shapedpolymer strips that were hydrated for at least 24 h in ddH₂O on anInstron 5542 (according to ASTM standard D412-98a). Differentialscanning calorimetry (DSC) was performed as previously reported (J. P.Bruggeman, C. J. Bettinger, C. L. E. Nijst, D. S. Kohane, R. Langer,Biodegradable Xylitol-Based Polymers. Adv Mater 2008). Briefly, glasstransition temperature (T_(g)) and other potential phase transitionswere measured within the temperature range of −90° C. and 250° C. with aheating/cooling rate of 10° C. per minute using a Q1000 DSC equippedwith Advantage Software v2.5 (TA Instruments, Newcastle, Del. USA) andanalyzed with Universal Analysis Software v4.3A (TA Instruments). Thechange of T_(g) over time (ΔT_(g)) was calculated by subtracting theT_(g) at the start of the experiment (T_(g, t=0)) with the T_(g) at timepoint t (T_(g, t=0)):ΔT _(g) =T _(g,t=0) −T _(g,t)  Equation 1

The mass density was measured using a pycnometer (Humboldt, MFG. CO),and crosslink density (n) as well as the relative molecular mass betweencrosslinks (M_(c)) were calculated from the following equations for anideal elastomer, where E₀ is the Young's modulus, R is the universal gasconstant, T is the temperature, and ρ is the mass density:

$\begin{matrix}{n = {\frac{E_{o}}{3{RT}} = \frac{\rho}{M_{c}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

The water-in-air contact angle measurements were carried out aspreviously mentioned (Y. Wang, G. A. Ameer, B. J. Sheppard, R. Langer, Atough biodegradable elastomer. Nat Biotechnol 2002, 20, (6), 602-606;incorporated herein by reference). Degradation of the explanted polymerswas determined by mass differential, calculated from the polymer's dryweight at t compared to the dry weight at the start of the study. Alldata are expressed as mean±standard deviation.

In Vivo Implantation of PXS Elastomers

Female Lewis rats (Charles River Laboratories, Wilmington, Mass.)weighing 200-250 g were housed in groups of 2 and had access to waterand food ad libitum. Animals were cared for according to the approvedprotocols of the Committee on Animal Care of the Massachusetts Instituteof Technology in conformity with the NIH guidelines for the care and useof laboratory animals (NIH publication #85-23, revised 1985). Theanimals were anaesthetized using continuous 2% isoflurane/O₂ inhalation.Two small midline incisions on the dorsum of the rat and the implantswere introduced in lateral subcutaneous pockets created by bluntdissection. The skin was closed using staples. Each rat carried eitherPXS 1:1 and PXS 1:2, or PXS 2:3 and 50/50 PXS 1:1/1:2, or PLGA implants.The animals were inspected daily until post-operative day 10 for anywound healing problems. Throughout the study, all rats stayed in goodgeneral health as assessed by their weight gain.

In Vivo Degradation and Biocompatibility of PXS Elastomers

For the degradation study, discs of photocured PXS elastomers (diameter10×1.6 mm) (n=4) were implanted subcutaneously in rats. Beforeimplantation, polymer discs were weighed (M₀) and their thickness (H₀)was measured between two glass cover slides using calipers. Toinvestigate in vivo degradation, implants were harvested atpre-determined time points and were collected in sterile saline.Directly upon surgical removal, the explants were dabbed dry, weighed(M_(wet)), and their thickness (H_(t)) was measured again. The explantswere then dried at 90° C. for 3 days and weighed (W_(dry)) again. Watercontent (hydration) by mass and implant dimensions over time werecalculated as follows:

$\begin{matrix}{\frac{M_{wet} - M_{dry}}{M_{dry}} \times 100\%} & {{Equation}\mspace{14mu} 3}\end{matrix}$for water content, and

$\begin{matrix}{\frac{{H_{t} - H_{0}}}{H_{0}} \times 100\%} & {{Equation}\mspace{14mu} 4}\end{matrix}$for implant size.

The mass loss over time was calculated using Equation 3.

$\begin{matrix}{\frac{M_{0} - M_{dry}}{M_{0}} \times 100\%} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Compression tests were performed on the wet explants with a 50N loadcell at a compression rate of 5 mm/min using an Instron 5542, accordingto ASTM standard D575-91. All samples were compressed to 20% and thecompression modulus was calculated from the initial slope (0-10%) of thestress-strain curve. The compression modulus was determined beforeimplantation, and the ratio of the initial modulus was calculated to themodulus at the pre-determined time point (E_(t)) as follows:

$\begin{matrix}{\frac{E_{t}}{E_{0}} \times 100\%} & {{Equation}\mspace{14mu} 6}\end{matrix}$Explants dedicated for scanning electron microscopy (SEM) weresputter-coated with platinum/palladium (≈250 A), mounted on aluminumstubs with carbon tape, and examined on a JEOL JSM-5910. Explantsdedicated to determine sol content were weighed (M_(dry)), placed in100% ethanol for 3 days on a orbital shaker, dried at 90° C. for 3 daysand weighed (M_(solfree)) again. The sol content of the explants wascalculated, using the following equation:

$\begin{matrix}{\frac{M_{dry} - M_{solfree}}{M_{solfree}} \times 100\%} & {{Equation}\mspace{14mu} 7}\end{matrix}$

For biocompatibility analysis, explants and surrounding tissues wereharvested, and fixed in Accustain for 24 h, dehydrated in graded ethanol(70-100%), embedded in paraffin, sectioned using a microtome (4 μm).Sequential sections (8-15 μm) were stained with hematoxilyn and eosin(H&E). The H&E stains were used to analyze for the presence offibroblasts and neutrophils in the tissues surrounding the material, andfor the presence of multinucleated giant cells, ingrowth of cells intothe material as well as phagocytosis of the material. Tissue macrophageswere identified by staining sections with primary rabbit anti-rat CD68(1:200, Abcam, England UK) (D. R. Greaves, S. Gordon,Macrophage-specific gene expression: current paradigms and futurechallenges. Int J Hematol. 2002, 76, (1), 6-15; incorporated herein byreference), followed by goat anti-mouse secondary antibody (VectorBurlingame, Calif. USA). Samples were incubated with streptavidinhorseradish peroxidase (1:100, Dako, Denmark) and developed with DABsubstrate chromogen (Dako). Histology images were recorded with a ZeissCCD Camera equipped with Axiovision software (Zeiss, Germany). At leastfour measurements were taken in ten random sections to calculate fibrouscapsule thickness and macrophage frequency.

Statistical Analysis

At least four fibrous capsule thickness measurements were made across atleast ten randomly selected images per sample. Histological macrophagescoring was also based on at least ten randomly selected images.Two-tailed student's t-tests with unequal variances were performed todetermine statistical significance, where appropriate (Microsoft Excel,Redmond, Wash. USA).

Results

Pre-Polymer Synthesis and Characterization

PXS pre-polymers were prepared by a polycondensation reaction betweenxylitol and sebacic acid in three stoichiometric ratios (FIG. 12A).Polymers with xylitol: sebacic acid ratios of 1:1, 2:3 and 1:2 wereprepared, designated PXS 1:1, PXS 2:3 and PXS 1:2 respectively. Chemicalcompositions were confirmed by ¹H-NMR spectra, as shown in Table 4below. Molecular weight distributions were determined by GPC for PXSpre-polymers, and are summarized in Table 4. As empirically determined,PXS pre-polymers have accessible melting temperatures (T_(m)s) andallowed for processing and mixing these pre-polymers. A blend of PXS 1:1and PXS 1:2 at 50/50 w/w was prepared and, similar to the PXS 1:1, PXS2:3 and PXS 1:2 pre-polymers, was further cured into elastomericnetworks (FIG. 12B).

TABLE 4 Composition T_(m) ^(a) M_(w) M_(n) Pre-polymer by ¹H-NMR (° C.)(g/mol) (g/mol) PDI PXS 1:1 1.0:0.91 80 2443 1268 1.9 PXS 1:1/1:21.0:1.56 90 4690 1689 2.8 PXS 2:3 1.0:1.63 100 3156 1117 2.7 PXS 1:21.0:1.85 100 6202 2255 2.7 ^(a)T_(m)s are temperatures where the polymerrevealed a transition from a white, opaque wax to a clear flowingliquid.Characterization of PXS Elastomers

PXS 1:1, PXS 2:3 and PXS 1:2 elastomers as well as a co-polymer of PXS1:1 and PXS 1:2 at 50/50 w/w (PXS 1:1/1:2) revealed stress strain curvesas shown in FIG. 13. Tensile Young's moduli ranged from 0.82±0.15 to5.33±0.40 MPa as previously reported for PXS 1:1 and PXS 1:2 elastomers(J. P. Bruggeman, C. J. Bettinger, C. L. E. Nijst, D. S. Kohane, R.Langer, Biodegradable Xylitol-Based Polymers. Adv Mater 2008). The PXS1:1/1:2 co-polymer and PXS 2:3 revealed Young's moduli of 2.32±0.27 and3.42±0.13 MPa respectively, and fall within the limits defined by PXS1:1 and 1:2. Mechanical properties of PXS elastomers are summarized inTable 5. Physical properties such as glass-transition temperatures(T_(g)s) and crosslink densities ranged from a lower limit defined byPXS 1:1 (7.3° C. and 10517.4±102.1 mol/m³), to upper limit values of PXS1:2 (22.9° C. and 1585.1±43.7 mol/m³) and in between these limits thevalues of PXS 1:1/1:2 (18.7° C. and 3685.7±90.5 mol/m³) and PXS 2:3(20.2° C. and 2521.6±100.5 mol/m³). The wettability of these elastomers,determined by contact angle measurements and hydration, showed a similartrend: PXS 1:1 exhibited the lowest contact angle and highest hydrationby mass (26.5±3.6° and 12.6±0.4%), PXS 1:2 the highest contact anglewith the lowest hydration (52.7±5.7° and 4.1±0.3%) and PXS 1:1/1:2 andPXS 2:3 (31.6±4.3°, 8.3±1.6% and 43.8±2.2°, 3.7±0.9% respectively) inbetween the values of PXS 1:1 and PXS 1:2. The physical properties ofPXS elastomers are summarized in Table 5.

TABLE 5 Young's Compression Contact Hydration Curing Modulus ModulusT_(g) angle by mass ρ n M_(c) Polymer process (MPa) (MPa) (° C.) (°) (%)(g/cm³) (mol/m³) (g/mol) PXS 1:1 120° C., 0.82 ± 0.15 1.67 ± 0.20 7.326.5 ± 3.6 12.6 ± 0.4 1.18 ± 0.02  112.2 ± 30.5 10517.4 ± 102.1 2 Pa, 4d PXS 120° C., 2.32 ± 0.27 2.67 ± 0.59 18.7 31.6 ± 4.3 8.3 ± 1.6 1.17 ±0.03 317.4 ± 21.0 3685.7 ± 90.5 1:1/1:2 2 Pa, 4 d PXS 2:3 120° C., 3.42± 0.13 3.71 ± 0.20 20.2 43.8 ± 2.2 3.7 ± 0.9 1.18 ± 0.01 468.0 ± 29.2 2521.6 ± 100.5 2 Pa, 4 d PXS 1:2 120° C., 5.33 ± 0.40 5.68 ± 0.56 22.952.7 ± 5.7 4.1 ± 0.3 1.16 ± 0.02 729.3 ± 57.3 1585.1 ± 43.7 2 Pa, 4 dIn Vivo Degradation of PXS Elastomers

Similar to the mechanical properties and physical characterization ofPXS elastomers, the in vivo mass loss, hydration by mass, construct solcontent, mechanical deterioration, and implant thickness, were alsoconfined to the outer limits that were defined by PXS 1:1 and PXS 1:2elastomers, and the values of the PXS 1:1/1:2 co-polymer and PXS 2:3elastomer within these limits. The in vivo half life of PXS 1:1 wasapproximately 3 to 4 weeks, and revealed a linear decrease in mass overtime (FIG. 14A). PXS 1:2 degraded much slower, with 76.7±3.7% of itsoriginal dry weight remaining at 28 weeks in vivo. In the first 12 weeksin vivo, PXS 1:2 did not show a decrease in mass at all (FIG. 14A). ThePXS 1:1/1:2 co-polymer appeared to have a mass loss profile that was acombination of the separate PXS 1:1 and PXS 1:2 elastomers: it had an invivo half life of ˜15 weeks and had almost completely degraded at 27weeks (FIG. 14A). The PXS 2:3 elastomer had a projected half life of ˜30weeks, and similar to the PXS 1:2 elastomer, showed an initial lag timewhere no mass loss was observed and after which a linear loss in masshad commenced (FIG. 14A).

Thermoset polymer networks can contain a fraction of loose, entangledmacromers that are not covalently attached to the polymer network,referred to as the sol fraction. Upon degradation of thermosetpolyesters, scission of esters bonds occurs, potentially changing anetwork's sol fraction. This behavior was observed for all PXSelastomers in vivo: sol fractions were observed to increase over time,being at their highest values near complete degradation, but neverexceeding 30% of its dry mass (FIG. 14A). However, sol fractions ofpolymers that showed the least mass loss never exceeded 10% of their drymass at that time (FIG. 14A, B).

ΔT_(g)s of PXS elastomers over time were initially negative, and thenincreased with time, as displayed for PXS 1:1/1:2, PXS 2:3 and PXS 1:2elastomers, as degradation occurred (FIG. 14C). The T_(g) measurementswere performed on sol-free, dry elastomers, and therefore only resemblethe thermal properties of the ‘naked’ degrading polymer network, withoutplasticizers such as water and other small molecules.

Implant thickness during degradation, as observed for all PXSelastomers, was shown to gradually decrease over time. This decrease wasthe most for PXS 1:1 and the least for PXS 1:2 (FIG. 14D). Hydration ofthe PXS elastomers was relatively mild and never exceeded 40% of theirdry mass (FIG. 14E). PXS 1:1 elastomers showed the highest hydrationduring their degradation. PXS 1:1/1:2, as well as the PXS 2:3 and PXS1:2 elastomers demonstrated similar trends in hydration as displayed inFIG. 14E.

Mechanical testing of the elastomers showed a decrease in Young'smodulus over time, except for PXS 1:2 elastomers (FIG. 14F). At23.3±3.7% mass loss of the PXS 1:2 elastomers, no deterioration inYoung's modulus was observed. When PXS 1:1 elastomers had degraded24.7±11.0% however, a decrease of 35.2±4.7% of their original mechanicalproperties was observed. The relationship between mass loss andmechanical properties is shown in FIG. 15, and demonstrates thedifferent trend for the PXS 1:2 elastomers in comparison to the otherPXS elastomers. Unlike PXS 1:2, the other polymers (PXS 1:1, PXS 2:3 andPXS 1:1/1:2) reveal a linear decrease of mechanical properties when thematerial degrades.

PXS elastomers maintain a high level of structural integrity and formstability, which seemed obvious when compared to a thermoplastic, suchas PLGA, which is known to swell up to 100-300% of its originaldimensions during degradation (FIG. 16A-J) (E. W. Henry, T. H. Chiu, E.Nyilas, T. M. Brushart, P. Dikkes, R. L. Sidman, Nerve regenerationthrough biodegradable polyester tubes. Exp Neurol. 1985, 90, 652-676; W.F. A. Den Dunnen, M. F. Meek, D. W. Grijpma, P. H. Robinson, J. M.Schakernraad, In vivo and in vitro degradation of poly[50/50(85/15L/D)LA/ε-CL], and the implications for the use in nerve reconstruction.J. Biomed. Mater. Res. A 2000, 51, 575-585); each of which isincorporated herein by reference).

Morphological Assessment of PXS and PLGA Implants

PXS elastomers appeared smooth-surfaced and optically clear at earlytime points upon visual inspection. Surfaces appeared progressivelyrough, and implants became more opaque as degradation occurred. SEManalysis of the surface as well as the interior of the implants revealeda degradation front that progressed inward from the surface for PXSelastomers (only PXS 1:1 and PXS 1:2 are shown) (FIG. 17A-F). After 1week, surfaces of PXS 1:1 elastomers showed excavates and the interiorof the implant seemed intact (FIG. 36A). When PXS 1:1 implants had lostmore than 76.7±3.7% of their initial mass, a more porous surface wasobserved (FIG. 17B). At 5 weeks in vivo, when PXS 1:2 elastomers had notshown mass loss, no changes were observed, either on their surface, noron the interior of the implant (FIG. 17C). Degrading PXS 1:2 elastomersalso demonstrated a rough, porous surface upon degradation, but thepores were smaller, compared to the PXS 1:1 surfaces (FIG. 36D). PLGAimplants were examined by SEM as well. PLGA implants degrade throughbulk degradation and this behavior was confirmed by SEM images: theinterior of PLGA implants showed signs of degradation, whereas thesurface did not (FIG. 17E, F).

In Vivo Biocompatibility of PXS 1:1 and 1:2 Elastomers

An initial biocompatibility study of PXS 1:1 and PXS 1:2 elastomers wasreported previously, and demonstrated competitive in vivobiocompatibility compared to PLGA implants (J. P. Bruggeman, C. J.Bettinger, C. L. E. Nijst, D. S. Kohane, R. Langer, BiodegradableXylitol-Based Polymers. Adv Mater 2008). Following implantation, none ofthe animals showed post-operative abnormalities in their wound healingprocess. At all time points during the in vivo experiment, all PXSimplants were encased by very thin, translucent fibrous capsules, andappeared thicker macroscopically for PLGA implants. On autopsy,occasional vascularization of the capsule was observed for PXS implants,but this seemed more obvious for PLGA implants. Clinically, thesurrounding tissues of the implants all appeared to be normal. At a lowmagnification (2.5×), the thin fibrous capsule surrounding PXS 1:1elastomers after 1 week in vivo is observed (FIG. 18A). When this wasexamined in more detail (black rectangular in FIG. 18A magnified 20×),this capsule seemed to consist mainly of lymphocytes, macrophages andfibroblasts (FIG. 18B). At a significant mass loss of PXS 1:1 elastomers(after 5 weeks in vivo), the degradation products did not seem toinfluence fibrous capsule thickness, as demonstrated in the lowmagnification overview in FIG. 18C. However, at 5 weeks, the fibrouscapsule showed signs of chronic inflammation with fewer lymphocytes,macrophages and giant cells at the polymer surface, as shown at 20×(FIG. 18D). The thin fibrous capsule was predominantly composedfibroblasts and vascularization of this capsule was not obvious. Fibrouscapsules surrounding the PXS 1:2 elastomers were comparable, despite theslower degradation rate. The acute inflammatory response was limited towhere the foreign material touched surrounding tissues, and the capsulein contact with the elastomer was thin, as shown at low magnification(FIG. 19A). At a higher magnification (FIG. 19B) lymphocytes,macrophages and fibroblasts were visible in this capsule, correspondingto a similar wound healing response as to the PXS 1:1 implants. As forPXS 1:1 elastomers, PXS 1:2 elastomers did not trigger noticeableinfiltration in the surrounding tissues, (FIG. 19B). After 28 weeks ofimplantation time, PXS 1:2 elastomers were still encased by a thinsurrounding fibrous capsule as shown in FIG. 19C. At the corners of theimplants, where most friction with surrounding tissues is expected, afibrous capsule of less than 20 cell layers thick was observed (FIG.19D). This fibrous capsule was mostly composed of fibroblasts with a fewscattered macrophages and giant cells at the polymer/tissue interface.After the first week in vivo, the capsules surrounding PLGA implantswere evidently vascularized (FIG. 20). In addition, tissues that werenot in direct contact with the implants seemed infiltrated withmononuclear cells (FIG. 20A, B). This response was almost absent for PXSelastomers. The initial wound healing response seemed to involve moremacrophages for PLGA implants (FIG. 20B) than observed for the PXSelastomers. Upon degradation of PLGA implants at 12 weeks in vivo, adifferent tissue response was observed, compared to PXS elastomers: amuch thicker fibrous capsule (FIG. 20C) that seemed to contain a highnumber of macrophages and giant cells as well as evident phagocytosis ofpolymer was observed (FIG. 20D).

When the sections were stained with antibodies against CD68, aqualitative difference was observed for PXS elastomers and PLGA polymers(FIG. 21A-I), as expected based on the H&E observations. When thesequalitative observations were quantified, a difference inbiocompatibility was noted between PXS elastomers and the PLGA polymer.FIG. 22A demonstrates the difference in fibrous capsule thicknesssurrounding the implants. Differences in percentage of activatedmacrophages (CD68+ cells) of the total surrounding cell population werealso significantly different between PXS and PGLA implants (FIG. 22B),showing that PXS elastomers did not recruit macrophages as was the casefor PLGA polymers.

Discussion

Tuning the in vivo behavior of thermoset PXS elastomers was possible byadjusting monomer feed ratio as well as by co-polymerization ofpre-polymers using different stoichiometries. Taking step-growth polymerkinetics into account, and using the hydroxyl groups as the dominantfunctionality by 1, the PXS 1:2 stoichiometry represented the maximumlimit of accessible crosslinking densities for PXS elastomers. As thenumber of aliphatic monomers in the polymerization reaction wereincreased to alter crosslink density, similar changes in glasstransition and tensile Young's modulus, as well as contact angles anddegradation rates were observed. Similar to reported degradation ratesfor FDA-approved thermoplastic polymers such as PLGA (J. C. Middleton,A. J. Tipton, Synthetic biodegradable polymers as orthopedic devices.Biomaterials 2000, 21, 2335-2346; incorporated herein by reference) andpoly( 50/50( 85/15 D/L)-lactic-co-ε-caprolactone) (W. F. A. Den Dunnen,M. F. Meek, D. W. Grijpma, P. H. Robinson, J. M. Schakernraad, In Vivoand in vitro degradation of poly[50/50(85/15 L/D)LA/s-CL], and theimplications for the use in nerve reconstruction. J Biomed Mater Res A2000, 51, 575-585; incorporated herein by reference), subcutaneousdegradation rates of PXS elastomers could be tuned from 7 weeks (PXS1:1), up to a projected life time of a little over 2 years (PXS 1:2)(FIG. 14A). These degradation rates were accessible for PXS elastomerswithout consequences in construct swelling (FIG. 14C) or form stabilityduring degradation (FIGS. 16 and 17). This is an important advantage forsmall-feature medical devices such as flexible drug eluting chips,sensors, peripheral nerve conduits, and small vascular grafts.

The mechanism by which thermoset PXS elastomers degraded in vivoappeared to be dominated by surface erosion, as demonstrated bymorphological studies (FIG. 17). As previously reported (J. P.Bruggeman, B. J. De Bruin, C. J. Bettinger, R. Langer, Synthesis andCharacterization of Biodegradable Poly(polyol sebacate) Polymers.Submitted 2008; incorporated herein by reference), PXS 1:1 and 1:2elastomers revealed in vitro mass losses of 1.78±0.30% and 1.88±0.22%respectively, after 105 days in PBS at 37° C. The obvious discrepancy ofthe in vitro mass loss versus the in vivo mass loss for PXS 1:1elastomers, may suggest that the surface erosion of PXS elastomers isenzyme-driven.

We observed an initial negative and subsequent positive in ΔT_(g) of PXSelastomers during degradation. A negative ΔT_(g) seems in accordancewith a bulk degrading profile, as a random cleavage of esters willpotentially decrease crosslink density, and thereby lowering the T_(g)of the material. However, when enzyme-driven surface erosion is assumed,an increase in T_(g) is expected to be observed: enzymes are most likelysterically shielded from cleaving esters within the bulk of the materialand may preferably cleave esters on the exposed, more mobile polymerchains. The observed in vivo kinetics of T_(g) suggest that bothdegradation mechanisms occur in vivo, but that surface degradation isthe most dominating profile with the highest rate.

The in vivo biocompatibility profile was comparable for PXS 1:1 and 1:2elastomers, which suggests that biocompatibility is constant across PXSmaterials with varied degradation rates and mechanical properties. PXSrevealed excellent biocompatibility when compared to PLGA, as PXSrecruited less macrophages and was encased by thinner fibrous capsules.

Conclusions

Biodegradable PXS elastomers enable precise control of materialproperties by adjusting the stoichiometric ratios as well as thepossibility of synthesizing co-polymers. A wide range of in vivodegradation rates and mechanical properties were achieved. In vivodegradation of PXS elastomers occurred primarily through surfaceerosion. PXS elastomers retained structural integrity and form stabilityduring degradation. PXS elastomers are biocompatible regardless ofdegradation rate and mechanical properties.

Other Embodiments

The foregoing has been a description of certain non-limiting preferredembodiments of the invention. Those of ordinary skill in the art willappreciate that various changes and modifications to this descriptionmay be made without departing from the spirit or scope of the presentinvention, as defined in the following claims.

What is claimed is:
 1. A polymer, wherein the backbone consists ofalternating polyol and polycarboxylic acid units, wherein: monomers usedto form the polymers are selected from the group consisting ofalkanedioic acids having two carboxylic acid groups and sugar alcoholscomprising at least four hydroxyl groups; and the ratio of the sugaralcohol units to the alkanedioic acid units in the polymer is 1 unit ofsugar alcohol to at least 2 units of alkanedioic acid.
 2. The polymeraccording to claim 1, wherein one or more of the hydroxyl groups havebeen modified with one or more acrylate moieties.
 3. The polymeraccording to claim 2, wherein the polymer is cross-linked viaconjugation of one or more of the acrylate moieties with one or morefree hydroxyl groups of the polymer.
 4. The polymer according to claim1, wherein the sugar alcohol is xylitol.
 5. The polymer according toclaim 1, wherein the alkanedioic acid is or comprises dimercaptosuccinicacid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, or sebacic acid.
 6. Thepolymer according to claim 1, wherein the sugar alcohol comprises atleast five (5) hydroxyl groups.
 7. The polymer according to claim 1,wherein the ratio of the sugar alcohol units to the alkanedioic acidunits in the polymer is 1 unit of sugar alcohol to 2 units ofalkanedioic acid.
 8. The polymer according to claim 1, wherein the sugaralcohol is erythritol, threitol, ribitol, arabinitol, xylitol, allitol,altritol, galactitol, sorbitol, mannitol, or iditol.
 9. The polymeraccording to claim 5, wherein the alkanedioic acid is sebacic acid orglutaric acid.
 10. The polymer according to claim 1, wherein the polymeris biodegradable.
 11. The polymer according to claim 1, wherein thealkanedioic acid is a C₈-C₁₂ alkanedioic acid.
 12. The polymer accordingto claim 1, wherein the polymer has an in-vivo half life of at least 8months.
 13. The polymer according to claim 1, wherein the polymerabsorbs between 0% to 9.5% water.
 14. The polymer according to claim 1,wherein the polymer has a Young's moduli of at least 0.5 to 12 MPa. 15.A polymer, wherein the backbone consists of alternating polyol andpolycarboxylic acid units, wherein: monomers used to form the polymersare selected from the group consisting of alkanedioic acids having twocarboxylic acid groups and sugar alcohols comprising at least fourhydroxyl groups; one or more of the hydroxyl groups in the polymer hasbeen modified with one or more acrylate moieties; and the ratio of thesugar alcohol units to the alkanedioic acid units in the polymer is 1unit of sugar alcohol to at least 2 units of alkanedioic acid.
 16. Thepolymer according to claim 15, wherein the alkanedioic acid isdimercaptosuccinic acid, oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, orsebacic acid.
 17. The polymer according to claim 15, wherein thealkanedioic acid is a C₈-C₁₂ alkanedioic acid.
 18. A polymer, whereinthe backbone consists of alternating sugar alcohol and alkanedioic acidunits, wherein: each sugar alcohol unit independently comprises at leastfour —O— moieties; each alkanedioic acid unit independently has thestructure of —C(O)(CH₂)_(x)C(O)—, wherein x is an integer of between 1to 20, inclusive, and each of the —(CH₂)— unit is optionally andindependently substituted; the ratio of the sugar alcohol units to thealkanedioic acid units in the polymer is 1 unit of sugar alcohol to atleast 2 units of alkanedioic acid.
 19. The polymer according to claim18, wherein the sugar alcohol unit comprises one or more free hydroxylgroups.
 20. The polymer according to claim 19, wherein one or more ofthe hydroxyl groups have been modified with one or more acrylatemoieties.
 21. The polymer according to claim 20, wherein the polymer iscross-linked via conjugation of one or more of the acrylate moietieswith one or more free hydroxyl groups of the polymer.
 22. The polymeraccording to claim 18, wherein the sugar alcohol is xylitol.
 23. Thepolymer according to claim 18, wherein x is 8-12.
 24. The polymer ofclaim 18, wherein the polymer is poly(xylitol-co-sebacate), wherein theratio of the xylitol units and the sebacate units is 1:2.